Clear user state in gprs (assign to zero) to reduce the influence of user
registers on speculation within kernel syscall handlers. Clears occur
at the very beginning of the sc and scv 0 interrupt handlers, with
restores occurring following the execution of the syscall handler.
Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
---
V1 -> V2: Update summary
V2 -> V3: Remove erroneous summary paragraph on syscall_exit_prepare
V3 -> V4: Use ZEROIZE instead of NULLIFY
---
arch/powerpc/kernel/interrupt_64.S | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/interrupt_64.S
b/arch/powerpc/kernel/interrupt_64.S
index 0178aeba3820..a8065209dd8c 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -70,7 +70,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
ld r2,PACATOC(r13)
mfcr r12
li r11,0
- /* Can we avoid saving r3-r8 in common case? */
+ /* Save syscall parameters in r3-r8 */
std r3,GPR3(r1)
std r4,GPR4(r1)
std r5,GPR5(r1)
@@ -109,6 +109,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
* but this is the best we can do.
*/
+ /*
+ * Zero user registers to prevent influencing speculative execution
+ * state of kernel code.
+ */
+ ZEROIZE_GPRS(5, 12)
+ ZEROIZE_NVGPRS()
+
/* Calling convention has r3 = orig r0, r4 = regs */
mr r3,r0
bl system_call_exception
@@ -139,6 +146,7 @@ BEGIN_FTR_SECTION
HMT_MEDIUM_LOW
END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
+ REST_NVGPRS(r1)
cmpdi r3,0
bne .Lsyscall_vectored_\name\()_restore_regs
@@ -181,7 +189,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
ld r4,_LINK(r1)
ld r5,_XER(r1)
- REST_NVGPRS(r1)
ld r0,GPR0(r1)
mtcr r2
mtctr r3
@@ -249,7 +256,7 @@ END_BTB_FLUSH_SECTION
ld r2,PACATOC(r13)
mfcr r12
li r11,0
- /* Can we avoid saving r3-r8 in common case? */
+ /* Save syscall parameters in r3-r8 */
std r3,GPR3(r1)
std r4,GPR4(r1)
std r5,GPR5(r1)
@@ -300,6 +307,13 @@ END_BTB_FLUSH_SECTION
wrteei 1
#endif
+ /*
+ * Zero user registers to prevent influencing speculative execution
+ * state of kernel code.
+ */
+ ZEROIZE_GPRS(5, 12)
+ ZEROIZE_NVGPRS()
+
/* Calling convention has r3 = orig r0, r4 = regs */
mr r3,r0
bl system_call_exception
@@ -342,6 +356,7 @@ BEGIN_FTR_SECTION
stdcx. r0,0,r1 /* to clear the reservation */
END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
+ REST_NVGPRS(r1)
cmpdi r3,0
bne .Lsyscall_restore_regs
/* Zero volatile regs that may contain sensitive kernel data */
@@ -377,7 +392,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
.Lsyscall_restore_regs:
ld r3,_CTR(r1)
ld r4,_XER(r1)
- REST_NVGPRS(r1)
mtctr r3
mtspr SPRN_XER,r4
ld r0,GPR0(r1)
--
2.34.1
