Zero GPRS r0, r2-r11, r14-r31, on entry into the kernel for all
other interrupt sources to limit influence of user-space values
in potential speculation gadgets. The remaining gprs are overwritten by
entry macros to interrupt handlers, irrespective of whether or not a
given handler consumes these register values.
Prior to this commit, r14-r31 are restored on a per-interrupt basis at
exit, but now they are always restored. Remove explicit REST_NVGPRS
invocations on interrupt entry and simplify exit logic. 32-bit systems
will still conditionally need to restore NVGPRS so keep return value for
interrupt_exit_user_prepare.
The mmap_bench benchmark in selftests should rapidly invoke pagefaults.
See ~0.8% performance regression with this mitigation, but this
indicates the worst-case performance due to heavier-weight interrupt
handlers.
Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
---
V1 -> V2: Add benchmark data
---
arch/powerpc/kernel/exceptions-64s.S | 21 ++++++++-------------
arch/powerpc/kernel/interrupt_64.S | 9 ++-------
2 files changed, 10 insertions(+), 20 deletions(-)
diff --git a/arch/powerpc/kernel/exceptions-64s.S
b/arch/powerpc/kernel/exceptions-64s.S
index 102896fc6a86..62dd6270852e 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -502,6 +502,7 @@ DEFINE_FIXED_SYMBOL(\name\()_common_real, text)
std r10,0(r1) /* make stack chain pointer */
std r0,GPR0(r1) /* save r0 in stackframe */
std r10,GPR1(r1) /* save r1 in stackframe */
+ NULLIFY_GPR(0)
/* Mark our [H]SRRs valid for return */
li r10,1
@@ -538,14 +539,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
ld r10,IAREA+EX_R10(r13)
std r9,GPR9(r1)
std r10,GPR10(r1)
+ NULLIFY_GPRS(9, 10)
ld r9,IAREA+EX_R11(r13) /* move r11 - r13 to stackframe */
ld r10,IAREA+EX_R12(r13)
ld r11,IAREA+EX_R13(r13)
std r9,GPR11(r1)
std r10,GPR12(r1)
std r11,GPR13(r1)
+ /* keep r12 ([H]SRR1/MSR), r13 (PACA) for interrupt routine */
+ NULLIFY_GPR(11)
SAVE_NVGPRS(r1)
+ NULLIFY_NVGPRS()
.if IDAR
.if IISIDE
@@ -577,8 +582,8 @@ BEGIN_FTR_SECTION
END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
ld r10,IAREA+EX_CTR(r13)
std r10,_CTR(r1)
- std r2,GPR2(r1) /* save r2 in stackframe */
- SAVE_GPRS(3, 8, r1) /* save r3 - r8 in stackframe */
+ SAVE_GPRS(2, 8, r1) /* save r2 - r8 in stackframe */
+ NULLIFY_GPRS(2, 8)
mflr r9 /* Get LR, later save to stack */
ld r2,PACATOC(r13) /* get kernel TOC into r2 */
std r9,_LINK(r1)
@@ -696,6 +701,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
mtlr r9
ld r9,_CCR(r1)
mtcr r9
+ REST_NVGPRS(r1)
REST_GPRS(2, 13, r1)
REST_GPR(0, r1)
/* restore original r1. */
@@ -1368,11 +1374,6 @@ ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
b interrupt_return_srr
1: bl do_break
- /*
- * do_break() may have changed the NV GPRS while handling a breakpoint.
- * If so, we need to restore them with their updated values.
- */
- REST_NVGPRS(r1)
b interrupt_return_srr
@@ -1598,7 +1599,6 @@ EXC_COMMON_BEGIN(alignment_common)
GEN_COMMON alignment
addi r3,r1,STACK_FRAME_OVERHEAD
bl alignment_exception
- REST_NVGPRS(r1) /* instruction emulation may change GPRs */
b interrupt_return_srr
@@ -1708,7 +1708,6 @@ EXC_COMMON_BEGIN(program_check_common)
.Ldo_program_check:
addi r3,r1,STACK_FRAME_OVERHEAD
bl program_check_exception
- REST_NVGPRS(r1) /* instruction emulation may change GPRs */
b interrupt_return_srr
@@ -2139,7 +2138,6 @@ EXC_COMMON_BEGIN(emulation_assist_common)
GEN_COMMON emulation_assist
addi r3,r1,STACK_FRAME_OVERHEAD
bl emulation_assist_interrupt
- REST_NVGPRS(r1) /* instruction emulation may change GPRs */
b interrupt_return_hsrr
@@ -2457,7 +2455,6 @@ EXC_COMMON_BEGIN(facility_unavailable_common)
GEN_COMMON facility_unavailable
addi r3,r1,STACK_FRAME_OVERHEAD
bl facility_unavailable_exception
- REST_NVGPRS(r1) /* instruction emulation may change GPRs */
b interrupt_return_srr
@@ -2485,7 +2482,6 @@ EXC_COMMON_BEGIN(h_facility_unavailable_common)
GEN_COMMON h_facility_unavailable
addi r3,r1,STACK_FRAME_OVERHEAD
bl facility_unavailable_exception
- REST_NVGPRS(r1) /* XXX Shouldn't be necessary in practice */
b interrupt_return_hsrr
@@ -2711,7 +2707,6 @@ EXC_COMMON_BEGIN(altivec_assist_common)
addi r3,r1,STACK_FRAME_OVERHEAD
#ifdef CONFIG_ALTIVEC
bl altivec_assist_exception
- REST_NVGPRS(r1) /* instruction emulation may change GPRs */
#else
bl unknown_exception
#endif
diff --git a/arch/powerpc/kernel/interrupt_64.S
b/arch/powerpc/kernel/interrupt_64.S
index efaf162fa772..083a94604072 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -430,9 +430,6 @@ interrupt_return_\srr\()_user: /* make backtraces match the
_kernel variant */
_ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user)
addi r3,r1,STACK_FRAME_OVERHEAD
bl interrupt_exit_user_prepare
- cmpdi r3,0
- bne- .Lrestore_nvgprs_\srr
-.Lrestore_nvgprs_\srr\()_cont:
std r1,PACA_EXIT_SAVE_R1(r13) /* save r1 for restart */
#ifdef CONFIG_PPC_BOOK3S
.Linterrupt_return_\srr\()_user_rst_start:
@@ -446,6 +443,7 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user)
stb r11,PACAIRQHAPPENED(r13) # clear out possible HARD_DIS
.Lfast_user_interrupt_return_\srr\():
+ REST_NVGPRS(r1)
#ifdef CONFIG_PPC_BOOK3S
.ifc \srr,srr
lbz r4,PACASRR_VALID(r13)
@@ -515,10 +513,6 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
b . /* prevent speculative execution */
.Linterrupt_return_\srr\()_user_rst_end:
-.Lrestore_nvgprs_\srr\():
- REST_NVGPRS(r1)
- b .Lrestore_nvgprs_\srr\()_cont
-
#ifdef CONFIG_PPC_BOOK3S
interrupt_return_\srr\()_user_restart:
_ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user_restart)
@@ -559,6 +553,7 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_kernel)
1:
.Lfast_kernel_interrupt_return_\srr\():
+ REST_NVGPRS(r1)
cmpdi cr1,r3,0
#ifdef CONFIG_PPC_BOOK3S
.ifc \srr,srr
--
2.34.1
