[PATCH v14 0/5] KVM: arm64: Provide guest support for GCS
The arm64 Guarded Control Stack (GCS) feature provides support for hardware protected stacks of return addresses, intended to provide hardening against return oriented programming (ROP) attacks and to make it easier to gather call stacks for applications such as profiling. When GCS is active a secondary stack called the Guarded Control Stack is maintained, protected with a memory attribute which means that it can only be written with specific GCS operations. The current GCS pointer can not be directly written to by userspace. When a BL is executed the value stored in LR is also pushed onto the GCS, and when a RET is executed the top of the GCS is popped and compared to LR with a fault being raised if the values do not match. GCS operations may only be performed on GCS pages, a data abort is generated if they are not. The combination of hardware enforcement and lack of extra instructions in the function entry and exit paths should result in something which has less overhead and is more difficult to attack than a purely software implementation like clang's shadow stacks. This series implements support for managing GCS for KVM guests, it also includes a fix for S1PIE which has also been sent separately as this feature is a dependency for GCS. It is based on: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/gcs Signed-off-by: Mark Brown --- Changes in v14: - Rebase onto arm64/for-next/gcs which includes all the non-KVM support. - Manage the fine grained traps for GCS instructions. - Manage PSTATE.EXLOCK when delivering exceptions to KVM guests. - Link to v13: https://lore.kernel.org/r/20241001-arm64-gcs-v13-0-222b78d87...@kernel.org Changes in v13: - Rebase onto v6.12-rc1. - Allocate VM_HIGH_ARCH_6 since protection keys used all the existing bits. - Implement mm_release() and free transparently allocated GCSs there. - Use bit 32 of AT_HWCAP for GCS due to AT_HWCAP2 being filled. - Since we now only set GCSCRE0_EL1 on change ensure that it is initialised with GCSPR_EL0 accessible to EL0. - Fix OOM handling on thread copy. - Link to v12: https://lore.kernel.org/r/20240829-arm64-gcs-v12-0-42fec9474...@kernel.org Changes in v12: - Clarify and simplify the signal handling code so we work with the register state. - When checking for write aborts to shadow stack pages ensure the fault is a data abort. - Depend on !UPROBES. - Comment cleanups. - Link to v11: https://lore.kernel.org/r/20240822-arm64-gcs-v11-0-41b81947e...@kernel.org Changes in v11: - Remove the dependency on the addition of clone3() support for shadow stacks, rebasing onto v6.11-rc3. - Make ID_AA64PFR1_EL1.GCS writeable in KVM. - Hide GCS registers when GCS is not enabled for KVM guests. - Require HCRX_EL2.GCSEn if booting at EL1. - Require that GCSCR_EL1 and GCSCRE0_EL1 be initialised regardless of if we boot at EL2 or EL1. - Remove some stray use of bit 63 in signal cap tokens. - Warn if we see a GCS with VM_SHARED. - Remove rdundant check for VM_WRITE in fault handling. - Cleanups and clarifications in the ABI document. - Clean up and improve documentation of some sync placement. - Only set the EL0 GCS mode if it's actually changed. - Various minor fixes and tweaks. - Link to v10: https://lore.kernel.org/r/20240801-arm64-gcs-v10-0-699e2bd21...@kernel.org Changes in v10: - Fix issues with THP. - Tighten up requirements for initialising GCSCR*. - Only generate GCS signal frames for threads using GCS. - Only context switch EL1 GCS registers if S1PIE is enabled. - Move context switch of GCSCRE0_EL1 to EL0 context switch. - Make GCS registers unconditionally visible to userspace. - Use FHU infrastructure. - Don't change writability of ID_AA64PFR1_EL1 for KVM. - Remove unused arguments from alloc_gcs(). - Typo fixes. - Link to v9: https://lore.kernel.org/r/20240625-arm64-gcs-v9-0-0f634469b...@kernel.org Changes in v9: - Rebase onto v6.10-rc3. - Restructure and clarify memory management fault handling. - Fix up basic-gcs for the latest clone3() changes. - Convert to newly merged KVM ID register based feature configuration. - Fixes for NV traps. - Link to v8: https://lore.kernel.org/r/20240203-arm64-gcs-v8-0-c9fec7767...@kernel.org Changes in v8: - Invalidate signal cap token on stack when consuming. - Typo and other trivial fixes. - Don't try to use process_vm_write() on GCS, it intentionally does not work. - Fix leak of thread GCSs. - Rebase onto latest clone3() series. - Link to v7: https://lore.kernel.org/r/20231122-arm64-gcs-v7-0-201c483bd...@kernel.org Changes in v7: - Rebase onto v6.7-rc2 via the clone3() patch series. - Change the token used to cap the stack during signal handling to be compatible with GCSPOPM. - Fix flags for new page types. - Fold in support for clone3(). - Replace copy_to_user_gcs() with put_user_gcs(). - Link to v6: https://lore.kernel.org/r/20231009-arm64-gcs-v6-0-78e55deaa...@kernel.org Changes in v6: - Rebase onto v6.6-rc3. - Add some more gcsb_dsync() barri
[PATCH v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an exception
As per DDI 0487 RWTXBY we need to manage PSTATE.EXLOCK when entering an
exception, when the exception is entered from a lower EL the bit is cleared
while if entering from the same EL it is set to GCSCR_ELx.EXLOCKEN.
Implement this behaviour in enter_exception64().
Signed-off-by: Mark Brown
---
arch/arm64/include/uapi/asm/ptrace.h | 2 ++
arch/arm64/kvm/hyp/exception.c | 10 ++
2 files changed, 12 insertions(+)
diff --git a/arch/arm64/include/uapi/asm/ptrace.h
b/arch/arm64/include/uapi/asm/ptrace.h
index
0f39ba4f3efd4a8760f0fca0fbf1a2563b191c7d..9987957f4f7137bf107653b817885bb976853a83
100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -37,6 +37,7 @@
#define PSR_MODE_EL3t 0x000c
#define PSR_MODE_EL3h 0x000d
#define PSR_MODE_MASK 0x000f
+#define PSR_EL_MASK0x000c
/* AArch32 CPSR bits */
#define PSR_MODE32_BIT 0x0010
@@ -56,6 +57,7 @@
#define PSR_C_BIT 0x2000
#define PSR_Z_BIT 0x4000
#define PSR_N_BIT 0x8000
+#define PSR_EXLOCK_BIT 0x4
#define PSR_BTYPE_SHIFT10
diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
index
424a5107cddb5e1cdd75ef3581adef03aaadabb7..0d41b9b75cf83250b2c0d20cd82c153869efb0e4
100644
--- a/arch/arm64/kvm/hyp/exception.c
+++ b/arch/arm64/kvm/hyp/exception.c
@@ -160,6 +160,16 @@ static void enter_exception64(struct kvm_vcpu *vcpu,
unsigned long target_mode,
// PSTATE.BTYPE is set to zero upon any exception to AArch64
// See ARM DDI 0487E.a, pages D1-2293 to D1-2294.
+ // PSTATE.EXLOCK is set to 0 upon any exception to a higher
+ // EL, or to GCSCR_ELx.EXLOCKEN for an exception to the same
+ // exception level. See ARM DDI 0487 RWTXBY, D.1.3.2 in K.a.
+ if (kvm_has_gcs(vcpu->kvm) &&
+ (target_mode & PSR_EL_MASK) == (mode & PSR_EL_MASK)) {
+ u64 gcscr = __vcpu_read_sys_reg(vcpu, GCSCR_EL1);
+ if (gcscr & GCSCR_ELx_EXLOCKEN)
+ new |= PSR_EXLOCK_BIT;
+ }
+
new |= PSR_D_BIT;
new |= PSR_A_BIT;
new |= PSR_I_BIT;
--
2.39.2
[PATCH v14 5/5] KVM: selftests: arm64: Add GCS registers to get-reg-list
GCS adds new registers GCSCR_EL1, GCSCRE0_EL1, GCSPR_EL1 and GCSPR_EL0. Add
these to those validated by get-reg-list.
Reviewed-by: Thiago Jung Bauermann
Signed-off-by: Mark Brown
---
tools/testing/selftests/kvm/aarch64/get-reg-list.c | 28 ++
1 file changed, 28 insertions(+)
diff --git a/tools/testing/selftests/kvm/aarch64/get-reg-list.c
b/tools/testing/selftests/kvm/aarch64/get-reg-list.c
index
d43fb3f49050ba3de950d19d56b45beefec9dbeb..c17451069a15d181bb5a7efc8963290828f58c4b
100644
--- a/tools/testing/selftests/kvm/aarch64/get-reg-list.c
+++ b/tools/testing/selftests/kvm/aarch64/get-reg-list.c
@@ -29,6 +29,24 @@ static struct feature_id_reg feat_id_regs[] = {
0,
1
},
+ {
+ ARM64_SYS_REG(3, 0, 2, 5, 0), /* GCSCR_EL1 */
+ ARM64_SYS_REG(3, 0, 0, 4, 1), /* ID_AA64PFR1_EL1 */
+ 44,
+ 1
+ },
+ {
+ ARM64_SYS_REG(3, 0, 2, 5, 1), /* GCSPR_EL1 */
+ ARM64_SYS_REG(3, 0, 0, 4, 1), /* ID_AA64PFR1_EL1 */
+ 44,
+ 1
+ },
+ {
+ ARM64_SYS_REG(3, 0, 2, 5, 2), /* GCSCRE0_EL1 */
+ ARM64_SYS_REG(3, 0, 0, 4, 1), /* ID_AA64PFR1_EL1 */
+ 44,
+ 1
+ },
{
ARM64_SYS_REG(3, 0, 10, 2, 2), /* PIRE0_EL1 */
ARM64_SYS_REG(3, 0, 0, 7, 3), /* ID_AA64MMFR3_EL1 */
@@ -52,6 +70,12 @@ static struct feature_id_reg feat_id_regs[] = {
ARM64_SYS_REG(3, 0, 0, 7, 3), /* ID_AA64MMFR3_EL1 */
16,
1
+ },
+ {
+ ARM64_SYS_REG(3, 3, 2, 5, 1), /* GCSPR_EL0 */
+ ARM64_SYS_REG(3, 0, 0, 4, 1), /* ID_AA64PFR1_EL1 */
+ 44,
+ 1
}
};
@@ -472,6 +496,9 @@ static __u64 base_regs[] = {
ARM64_SYS_REG(3, 0, 2, 0, 1), /* TTBR1_EL1 */
ARM64_SYS_REG(3, 0, 2, 0, 2), /* TCR_EL1 */
ARM64_SYS_REG(3, 0, 2, 0, 3), /* TCR2_EL1 */
+ ARM64_SYS_REG(3, 0, 2, 5, 0), /* GCSCR_EL1 */
+ ARM64_SYS_REG(3, 0, 2, 5, 1), /* GCSPR_EL1 */
+ ARM64_SYS_REG(3, 0, 2, 5, 2), /* GCSCRE0_EL1 */
ARM64_SYS_REG(3, 0, 5, 1, 0), /* AFSR0_EL1 */
ARM64_SYS_REG(3, 0, 5, 1, 1), /* AFSR1_EL1 */
ARM64_SYS_REG(3, 0, 5, 2, 0), /* ESR_EL1 */
@@ -488,6 +515,7 @@ static __u64 base_regs[] = {
ARM64_SYS_REG(3, 0, 13, 0, 4), /* TPIDR_EL1 */
ARM64_SYS_REG(3, 0, 14, 1, 0), /* CNTKCTL_EL1 */
ARM64_SYS_REG(3, 2, 0, 0, 0), /* CSSELR_EL1 */
+ ARM64_SYS_REG(3, 3, 2, 5, 1), /* GCSPR_EL0 */
ARM64_SYS_REG(3, 3, 10, 2, 4), /* POR_EL0 */
ARM64_SYS_REG(3, 3, 13, 0, 2), /* TPIDR_EL0 */
ARM64_SYS_REG(3, 3, 13, 0, 3), /* TPIDRRO_EL0 */
--
2.39.2
[PATCH v14 1/5] KVM: arm64: Expose S1PIE to guests
Prior to commit 70ed7238297f ("KVM: arm64: Sanitise ID_AA64MMFR3_EL1")
we just exposed the santised view of ID_AA64MMFR3_EL1 to guests, meaning
that they saw both TCRX and S1PIE if present on the host machine. That
commit added VMM control over the contents of the register and exposed
S1POE but removed S1PIE, meaning that the extension is no longer visible
to guests. Reenable support for S1PIE with VMM control.
Fixes: 70ed7238297f ("KVM: arm64: Sanitise ID_AA64MMFR3_EL1")
Signed-off-by: Mark Brown
---
arch/arm64/kvm/sys_regs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index
dad88e31f9537fe02e28b117d6a740f15572e0ba..d48f89ad6aa7139078e7991ce6c8ebc4a0543551
100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1550,7 +1550,8 @@ static u64 __kvm_read_sanitised_id_reg(const struct
kvm_vcpu *vcpu,
val &= ~ID_AA64MMFR2_EL1_CCIDX_MASK;
break;
case SYS_ID_AA64MMFR3_EL1:
- val &= ID_AA64MMFR3_EL1_TCRX | ID_AA64MMFR3_EL1_S1POE;
+ val &= ID_AA64MMFR3_EL1_TCRX | ID_AA64MMFR3_EL1_S1POE |
+ ID_AA64MMFR3_EL1_S1PIE;
break;
case SYS_ID_MMFR4_EL1:
val &= ~ARM64_FEATURE_MASK(ID_MMFR4_EL1_CCIDX);
@@ -2433,6 +2434,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
ID_AA64MMFR2_EL1_NV |
ID_AA64MMFR2_EL1_CCIDX)),
ID_WRITABLE(ID_AA64MMFR3_EL1, (ID_AA64MMFR3_EL1_TCRX|
+ ID_AA64MMFR3_EL1_S1PIE |
ID_AA64MMFR3_EL1_S1POE)),
ID_SANITISED(ID_AA64MMFR4_EL1),
ID_UNALLOCATED(7,5),
--
2.39.2
[PATCH v14 2/5] arm64/gcs: Ensure FGTs for EL1 GCS instructions are disabled
The initial EL2 setup for GCS did not include disabling of EL1 usage of GCS instructions, also disable these traps. This is the first disabling of instruction traps, use x2 to store the value to be written. Signed-off-by: Mark Brown --- arch/arm64/include/asm/el2_setup.h | 7 ++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h index 27086a81eae34483a682681ab1be1959a339527a..99e887a5b2190f8810f1ed22d35b7acd26d2fd1e 100644 --- a/arch/arm64/include/asm/el2_setup.h +++ b/arch/arm64/include/asm/el2_setup.h @@ -170,6 +170,7 @@ cbz x1, .Lskip_fgt_\@ mov x0, xzr + mov x2, xzr mrs x1, id_aa64dfr0_el1 ubfxx1, x1, #ID_AA64DFR0_EL1_PMSVer_SHIFT, #4 cmp x1, #3 @@ -217,10 +218,14 @@ orr x0, x0, #HFGxTR_EL2_nGCS_EL1_MASK orr x0, x0, #HFGxTR_EL2_nGCS_EL0_MASK + orr x2, x2, #HFGITR_EL2_nGCSEPP_MASK + orr x2, x2, #HFGITR_EL2_nGCSSTR_EL1_MASK + orr x2, x2, #HFGITR_EL2_nGCSPUSHM_EL1_MASK + .Lset_fgt_\@: msr_s SYS_HFGRTR_EL2, x0 msr_s SYS_HFGWTR_EL2, x0 - msr_s SYS_HFGITR_EL2, xzr + msr_s SYS_HFGITR_EL2, x2 mrs x1, id_aa64pfr0_el1 // AMU traps UNDEF without AMU ubfxx1, x1, #ID_AA64PFR0_EL1_AMU_SHIFT, #4 -- 2.39.2
[PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
GCS introduces a number of system registers for EL1 and EL0, on systems
with GCS we need to context switch them and expose them to VMMs to allow
guests to use GCS.
In order to allow guests to use GCS we also need to configure
HCRX_EL2.GCSEn, if this is not set GCS instructions will be noops and
CHKFEAT will report GCS as disabled. Also enable fine grained traps for
access to the GCS registers by guests which do not have the feature
enabled.
In order to allow userspace to control availability of the feature to
guests we enable writability for only ID_AA64PFR1_EL1.GCS, this is a
deliberately conservative choice to avoid errors due to oversights.
Further fields should be made writable in future.
Signed-off-by: Mark Brown
---
arch/arm64/include/asm/kvm_host.h | 12
arch/arm64/include/asm/vncr_mapping.h | 2 ++
arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 31 ++
arch/arm64/kvm/sys_regs.c | 31 +-
4 files changed, 75 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/kvm_host.h
b/arch/arm64/include/asm/kvm_host.h
index
329619c6fa9611b474dc4823fccf01a3b9dd61a8..31887d3f3de18bf1936ce4329256894f6210c67e
100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -448,6 +448,10 @@ enum vcpu_sysreg {
POR_EL0,/* Permission Overlay Register 0 (EL0) */
+ /* Guarded Control Stack registers */
+ GCSCRE0_EL1,/* Guarded Control Stack Control (EL0) */
+ GCSPR_EL0, /* Guarded Control Stack Pointer (EL0) */
+
/* FP/SIMD/SVE */
SVCR,
FPMR,
@@ -525,6 +529,10 @@ enum vcpu_sysreg {
VNCR(POR_EL1), /* Permission Overlay Register 1 (EL1) */
+ /* Guarded Control Stack registers */
+ VNCR(GCSPR_EL1),/* Guarded Control Stack Pointer (EL1) */
+ VNCR(GCSCR_EL1),/* Guarded Control Stack Control (EL1) */
+
VNCR(HFGRTR_EL2),
VNCR(HFGWTR_EL2),
VNCR(HFGITR_EL2),
@@ -1495,4 +1503,8 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
(system_supports_fpmr() && \
kvm_has_feat((k), ID_AA64PFR2_EL1, FPMR, IMP))
+#define kvm_has_gcs(k) \
+ (system_supports_gcs() && \
+kvm_has_feat((k), ID_AA64PFR1_EL1, GCS, IMP))
+
#endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/include/asm/vncr_mapping.h
b/arch/arm64/include/asm/vncr_mapping.h
index
06f8ec0906a6e92b6dd57c692e1293ac3d4244fd..e289064148b3268a00830c6fee708029c4c0fbbb
100644
--- a/arch/arm64/include/asm/vncr_mapping.h
+++ b/arch/arm64/include/asm/vncr_mapping.h
@@ -89,6 +89,8 @@
#define VNCR_PMSIRR_EL1 0x840
#define VNCR_PMSLATFR_EL1 0x848
#define VNCR_TRFCR_EL1 0x880
+#define VNCR_GCSPR_EL1 0x8C0
+#define VNCR_GCSCR_EL1 0x8D0
#define VNCR_MPAM1_EL1 0x900
#define VNCR_MPAMHCR_EL20x930
#define VNCR_MPAMVPMV_EL2 0x938
diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
index
1579a3c08a36b989fec7fdc3f38b64cb498326f3..70bd6143083439d75387eccc17f5c3811c689047
100644
--- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
+++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
@@ -17,6 +17,7 @@
#include
static inline bool ctxt_has_s1poe(struct kvm_cpu_context *ctxt);
+static inline bool ctxt_has_gcs(struct kvm_cpu_context *ctxt);
static inline void __sysreg_save_common_state(struct kvm_cpu_context *ctxt)
{
@@ -31,6 +32,11 @@ static inline void __sysreg_save_user_state(struct
kvm_cpu_context *ctxt)
{
ctxt_sys_reg(ctxt, TPIDR_EL0) = read_sysreg(tpidr_el0);
ctxt_sys_reg(ctxt, TPIDRRO_EL0) = read_sysreg(tpidrro_el0);
+
+ if (ctxt_has_gcs(ctxt)) {
+ ctxt_sys_reg(ctxt, GCSPR_EL0) = read_sysreg_s(SYS_GCSPR_EL0);
+ ctxt_sys_reg(ctxt, GCSCRE0_EL1) =
read_sysreg_s(SYS_GCSCRE0_EL1);
+ }
}
static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt)
@@ -83,6 +89,17 @@ static inline bool ctxt_has_s1poe(struct kvm_cpu_context
*ctxt)
return kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64MMFR3_EL1, S1POE,
IMP);
}
+static inline bool ctxt_has_gcs(struct kvm_cpu_context *ctxt)
+{
+ struct kvm_vcpu *vcpu;
+
+ if (!cpus_have_final_cap(ARM64_HAS_GCS))
+ return false;
+
+ vcpu = ctxt_to_vcpu(ctxt);
+ return kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64PFR1_EL1, GCS, IMP);
+}
+
static inline void __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
{
ctxt_sys_reg(ctxt, SCTLR_EL1) = read_sysreg_el1(SYS_SCTLR);
@@ -96,6 +113,10 @@ static inline void __sysreg_save_el1_state(struct
kvm_cpu_context *ctxt)
if (ctxt_has_s1pie(ctxt)) {
ctxt_sys_reg(ctxt, PIR_EL1) =
read_sysreg_el1(SYS_PIR);
ct
Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, Oct 05, 2024 at 02:18:57PM +0100, Marc Zyngier wrote: > Mark Brown wrote: > > On Sat, Oct 05, 2024 at 12:34:20PM +0100, Marc Zyngier wrote: > > > Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1? > > These will trap with an EC of 0x2d which isn't known so I was expecting > > this to get handled in the same way as for example a return of false > > from kvm_hyp_handle_fpsimd() for SVE when unsupported, or for the > > simiarly unknown SME EC, currently. I gather from your comment that > > you're instead expecting to see an explicit exit handler for this EC > > that just injects the UNDEF directly? > Not just inject an UNDEF directly, but also track whether this needs > to be forwarded when the guest's HFGITR_EL2.nGCSSTR_EL1 is 0 while not > being not RES0. Basically following what the pseudocode describes. Ah, I see. I'd been under the impression that the generic machinery was supposed to handle this already using the descriptions in emulate-nested.c and we only needed handlers for more specific actions. signature.asc Description: PGP signature
Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, Oct 05, 2024 at 03:02:09PM +0100, Marc Zyngier wrote: > Mark Brown wrote: > > Ah, I see. I'd been under the impression that the generic machinery was > > supposed to handle this already using the descriptions in > > emulate-nested.c and we only needed handlers for more specific actions. > From that very file: > /* > * Map encoding to trap bits for exception reported with EC=0x18. > [...] > */ > Everything else needs special handling. I see. I had noticed that comment on that table but I didn't register that the comment wound up applying to the whole file rather than being about a specific part of the handling. I'm a bit confused about how things like the SVE traps I mentioned work here... signature.asc Description: PGP signature
Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, 05 Oct 2024 15:26:38 +0100, Mark Brown wrote: > > [1 ] > On Sat, Oct 05, 2024 at 03:02:09PM +0100, Marc Zyngier wrote: > > Mark Brown wrote: > > > > Ah, I see. I'd been under the impression that the generic machinery was > > > supposed to handle this already using the descriptions in > > > emulate-nested.c and we only needed handlers for more specific actions. > > > From that very file: > > > /* > > * Map encoding to trap bits for exception reported with EC=0x18. > > [...] > > */ > > > Everything else needs special handling. > > I see. I had noticed that comment on that table but I didn't register > that the comment wound up applying to the whole file rather than being > about a specific part of the handling. I'm a bit confused about how > things like the SVE traps I mentioned work here... Like all ECs, the handling starts in handle_exit.c. M. -- Without deviation from the norm, progress is not possible.
Re: [PATCH v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an exception
On Sat, Oct 05, 2024 at 01:36:09PM +0100, Marc Zyngier wrote:
> Mark Brown wrote:
> > + // PSTATE.EXLOCK is set to 0 upon any exception to a higher
> > + // EL, or to GCSCR_ELx.EXLOCKEN for an exception to the same
> > + // exception level. See ARM DDI 0487 RWTXBY, D.1.3.2 in K.a.
> > + if (kvm_has_gcs(vcpu->kvm) &&
> > + (target_mode & PSR_EL_MASK) == (mode & PSR_EL_MASK)) {
> > + u64 gcscr = __vcpu_read_sys_reg(vcpu, GCSCR_EL1);
> No, please. This only works by luck when a guest has AArch32 EL0, and
> creates more havoc on a NV guest. In general, this PSR_EL_MASK creates
> more problem than anything else, and doesn't fit the rest of the code.
You say luck, I say careful architecture definition but sure.
> So this needs to:
> - explicitly only apply to exceptions from AArch64
> - handle exception from EL2, since this helper already deals with that
> The latter point of course means introducing GCSCR_EL2 (and everything
> that depends on it, such as the trap handling).
For clarity, which trap handling specifically?
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Re: [PATCH v2 1/6] Add AutoFDO support for Clang build
Kees Cook writes: > The tradition in kernel .rst is to do this with the trailing "::", e.g.: > > +Configure the kernel with:: > + > + CONFIG_AUTOFDO_CLANG=y > > This loses the language-specific highlighting when rendered. Perhaps the > "::" extension can be further extended? > > +Configure the kernel with::(make) > + > + CONFIG_AUTOFDO_CLANG=y > > Then we could avoid the extra 2 lines but still gain the rendered language > highlights? The :: notation is standard Sphinx, not an extension we have done. So the proposed syntax would have to be done from the beginning, I'm not sure how easy or hard that would be, or whether it would be worth it. But then, I've always seen relatively little value in the highlighting; others clearly differ. Thanks, jon
Re: [PATCH v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an exception
On Sat, 05 Oct 2024 15:14:21 +0100,
Mark Brown wrote:
>
> On Sat, Oct 05, 2024 at 01:36:09PM +0100, Marc Zyngier wrote:
> > Mark Brown wrote:
>
> > > + // PSTATE.EXLOCK is set to 0 upon any exception to a higher
> > > + // EL, or to GCSCR_ELx.EXLOCKEN for an exception to the same
> > > + // exception level. See ARM DDI 0487 RWTXBY, D.1.3.2 in K.a.
> > > + if (kvm_has_gcs(vcpu->kvm) &&
> > > + (target_mode & PSR_EL_MASK) == (mode & PSR_EL_MASK)) {
> > > + u64 gcscr = __vcpu_read_sys_reg(vcpu, GCSCR_EL1);
>
> > No, please. This only works by luck when a guest has AArch32 EL0, and
> > creates more havoc on a NV guest. In general, this PSR_EL_MASK creates
> > more problem than anything else, and doesn't fit the rest of the code.
>
> You say luck, I say careful architecture definition but sure.
I wasn't talking about the architecture, but sure.
>
> > So this needs to:
> > - explicitly only apply to exceptions from AArch64
> > - handle exception from EL2, since this helper already deals with that
>
> > The latter point of course means introducing GCSCR_EL2 (and everything
> > that depends on it, such as the trap handling).
>
> For clarity, which trap handling specifically?
All the traps described in the GCSCR_EL2 documentation -- I see two
control bits described in K.a, all of which needs to be propagated and
their effects handled. Similarly, GCSPR_EL2 needs to be defined.
M.
--
Without deviation from the norm, progress is not possible.
Re: [PATCH v2 1/6] Add AutoFDO support for Clang build
On Fri, Oct 04, 2024 at 02:23:45PM -0700, Justin Stitt wrote: > On Fri, Oct 4, 2024 at 11:29 AM Peter Zijlstra wrote: > > > > On Fri, Oct 04, 2024 at 11:10:04AM -0700, Kees Cook wrote: > > > > > +Configure the kernel with::(make) > > > + > > > + CONFIG_AUTOFDO_CLANG=y > > > > > > Then we could avoid the extra 2 lines but still gain the rendered language > > > highlights? > > > > The whole double-colon thing is already a pain to read; you're making it > > worse again. > > Lots of people read docs on the web and having code blocks with > monospaced fonts (+syntax highlighting) makes them easier to read > there. > > Configure the kernel with: > > CONFIG_AUTOFDO_CLANG=y > > --versus-- > > Configure the kernel with:: > > CONFIG_AUTOFDO_CLANG=y > > This renders better for html through Sphinx and really can't be that > bad to read in vim, can it? It's weird; but I've gotten sorta used to it. I was more or less commenting on Kees' proposal of making it: Configure the kernel with::(make) Which is definitely harder to read since it insta triggers a syntax error exception in my head.
Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, 05 Oct 2024 11:37:30 +0100,
Mark Brown wrote:
>
> GCS introduces a number of system registers for EL1 and EL0, on systems
> with GCS we need to context switch them and expose them to VMMs to allow
> guests to use GCS.
>
> In order to allow guests to use GCS we also need to configure
> HCRX_EL2.GCSEn, if this is not set GCS instructions will be noops and
> CHKFEAT will report GCS as disabled. Also enable fine grained traps for
> access to the GCS registers by guests which do not have the feature
> enabled.
>
> In order to allow userspace to control availability of the feature to
> guests we enable writability for only ID_AA64PFR1_EL1.GCS, this is a
> deliberately conservative choice to avoid errors due to oversights.
> Further fields should be made writable in future.
It appears I have accidentally dropped the branch fixing
ID_AA64PFR1_EL1. I'll make sure this goes in as quickly as possible.
>
> Signed-off-by: Mark Brown
> ---
> arch/arm64/include/asm/kvm_host.h | 12
> arch/arm64/include/asm/vncr_mapping.h | 2 ++
> arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 31
> ++
> arch/arm64/kvm/sys_regs.c | 31
> +-
> 4 files changed, 75 insertions(+), 1 deletion(-)
>
[...]
> @@ -4716,6 +4737,14 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
> kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nPOR_EL1 |
> HFGxTR_EL2_nPOR_EL0);
>
> + if (!kvm_has_gcs(kvm)) {
> + kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
> + HFGxTR_EL2_nGCS_EL1);
> + kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_nGCSEPP |
> + HFGITR_EL2_nGCSSTR_EL1 |
> + HFGITR_EL2_nGCSPUSHM_EL1);
Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1?
M.
--
Without deviation from the norm, progress is not possible.
Re: [PATCH v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an exception
On Sat, 05 Oct 2024 11:37:31 +0100,
Mark Brown wrote:
>
> As per DDI 0487 RWTXBY we need to manage PSTATE.EXLOCK when entering an
> exception, when the exception is entered from a lower EL the bit is cleared
> while if entering from the same EL it is set to GCSCR_ELx.EXLOCKEN.
> Implement this behaviour in enter_exception64().
>
> Signed-off-by: Mark Brown
> ---
> arch/arm64/include/uapi/asm/ptrace.h | 2 ++
> arch/arm64/kvm/hyp/exception.c | 10 ++
> 2 files changed, 12 insertions(+)
>
> diff --git a/arch/arm64/include/uapi/asm/ptrace.h
> b/arch/arm64/include/uapi/asm/ptrace.h
> index
> 0f39ba4f3efd4a8760f0fca0fbf1a2563b191c7d..9987957f4f7137bf107653b817885bb976853a83
> 100644
> --- a/arch/arm64/include/uapi/asm/ptrace.h
> +++ b/arch/arm64/include/uapi/asm/ptrace.h
> @@ -37,6 +37,7 @@
> #define PSR_MODE_EL3t0x000c
> #define PSR_MODE_EL3h0x000d
> #define PSR_MODE_MASK0x000f
> +#define PSR_EL_MASK 0x000c
>
> /* AArch32 CPSR bits */
> #define PSR_MODE32_BIT 0x0010
> @@ -56,6 +57,7 @@
> #define PSR_C_BIT0x2000
> #define PSR_Z_BIT0x4000
> #define PSR_N_BIT0x8000
> +#define PSR_EXLOCK_BIT 0x4
>
> #define PSR_BTYPE_SHIFT 10
>
> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
> index
> 424a5107cddb5e1cdd75ef3581adef03aaadabb7..0d41b9b75cf83250b2c0d20cd82c153869efb0e4
> 100644
> --- a/arch/arm64/kvm/hyp/exception.c
> +++ b/arch/arm64/kvm/hyp/exception.c
> @@ -160,6 +160,16 @@ static void enter_exception64(struct kvm_vcpu *vcpu,
> unsigned long target_mode,
> // PSTATE.BTYPE is set to zero upon any exception to AArch64
> // See ARM DDI 0487E.a, pages D1-2293 to D1-2294.
>
> + // PSTATE.EXLOCK is set to 0 upon any exception to a higher
> + // EL, or to GCSCR_ELx.EXLOCKEN for an exception to the same
> + // exception level. See ARM DDI 0487 RWTXBY, D.1.3.2 in K.a.
> + if (kvm_has_gcs(vcpu->kvm) &&
> + (target_mode & PSR_EL_MASK) == (mode & PSR_EL_MASK)) {
> + u64 gcscr = __vcpu_read_sys_reg(vcpu, GCSCR_EL1);
No, please. This only works by luck when a guest has AArch32 EL0, and
creates more havoc on a NV guest. In general, this PSR_EL_MASK creates
more problem than anything else, and doesn't fit the rest of the code.
So this needs to:
- explicitly only apply to exceptions from AArch64
- handle exception from EL2, since this helper already deals with that
The latter point of course means introducing GCSCR_EL2 (and everything
that depends on it, such as the trap handling).
M.
--
Without deviation from the norm, progress is not possible.
Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, Oct 05, 2024 at 12:34:20PM +0100, Marc Zyngier wrote:
> Mark Brown wrote:
> > + if (!kvm_has_gcs(kvm)) {
> > + kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
> > + HFGxTR_EL2_nGCS_EL1);
> > + kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_nGCSEPP |
> > + HFGITR_EL2_nGCSSTR_EL1 |
> > + HFGITR_EL2_nGCSPUSHM_EL1);
> Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1?
These will trap with an EC of 0x2d which isn't known so I was expecting
this to get handled in the same way as for example a return of false
from kvm_hyp_handle_fpsimd() for SVE when unsupported, or for the
simiarly unknown SME EC, currently. I gather from your comment that
you're instead expecting to see an explicit exit handler for this EC
that just injects the UNDEF directly?
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Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, 05 Oct 2024 14:08:39 +0100,
Mark Brown wrote:
>
> On Sat, Oct 05, 2024 at 12:34:20PM +0100, Marc Zyngier wrote:
> > Mark Brown wrote:
>
> > > + if (!kvm_has_gcs(kvm)) {
> > > + kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
> > > + HFGxTR_EL2_nGCS_EL1);
> > > + kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_nGCSEPP |
> > > + HFGITR_EL2_nGCSSTR_EL1 |
> > > + HFGITR_EL2_nGCSPUSHM_EL1);
>
> > Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1?
>
> These will trap with an EC of 0x2d which isn't known so I was expecting
> this to get handled in the same way as for example a return of false
> from kvm_hyp_handle_fpsimd() for SVE when unsupported, or for the
> simiarly unknown SME EC, currently. I gather from your comment that
> you're instead expecting to see an explicit exit handler for this EC
> that just injects the UNDEF directly?
Not just inject an UNDEF directly, but also track whether this needs
to be forwarded when the guest's HFGITR_EL2.nGCSSTR_EL1 is 0 while not
being not RES0. Basically following what the pseudocode describes.
M.
--
Without deviation from the norm, progress is not possible.
Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests
On Sat, 05 Oct 2024 14:48:09 +0100, Mark Brown wrote: > > [1 ] > On Sat, Oct 05, 2024 at 02:18:57PM +0100, Marc Zyngier wrote: > > Mark Brown wrote: > > > On Sat, Oct 05, 2024 at 12:34:20PM +0100, Marc Zyngier wrote: > > > > > Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1? > > > > These will trap with an EC of 0x2d which isn't known so I was expecting > > > this to get handled in the same way as for example a return of false > > > from kvm_hyp_handle_fpsimd() for SVE when unsupported, or for the > > > simiarly unknown SME EC, currently. I gather from your comment that > > > you're instead expecting to see an explicit exit handler for this EC > > > that just injects the UNDEF directly? > > > Not just inject an UNDEF directly, but also track whether this needs > > to be forwarded when the guest's HFGITR_EL2.nGCSSTR_EL1 is 0 while not > > being not RES0. Basically following what the pseudocode describes. > > Ah, I see. I'd been under the impression that the generic machinery was > supposed to handle this already using the descriptions in > emulate-nested.c and we only needed handlers for more specific actions. From that very file: /* * Map encoding to trap bits for exception reported with EC=0x18. [...] */ Everything else needs special handling. M. -- Without deviation from the norm, progress is not possible.
