[PATCH v6 22/25] powerpc/64s: Clear user GPRs in syscall interrupt entry
From: Rohan McLure <hidden>
Date: 2022-09-21 07:12:17
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
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 <redacted> --- V2: Update summary V3: Remove erroneous summary paragraph on syscall_exit_prepare V4: Use ZEROIZE instead of NULLIFY. Clear r0 also. V5: Move to end of patch series. V6: Include clears which were previously in the syscall wrapper patch. Move comment on r3-r8 register save to when we alter the calling convention for system_call_exception. --- arch/powerpc/kernel/interrupt_64.S | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index a5dd78bdbe6d..40147558e1a6 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S@@ -106,6 +106,13 @@ 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_GPR(0) + ZEROIZE_GPRS(5, 12) + ZEROIZE_NVGPRS() bl system_call_exception .Lsyscall_vectored_\name\()_exit:
@@ -134,6 +141,7 @@ 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
@@ -285,6 +293,13 @@ END_BTB_FLUSH_SECTION wrteei 1 #endif + /* + * Zero user registers to prevent influencing speculative execution + * state of kernel code. + */ + ZEROIZE_GPR(0) + ZEROIZE_GPRS(5, 12) + ZEROIZE_NVGPRS() bl system_call_exception .Lsyscall_exit:
@@ -325,6 +340,7 @@ 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 */
@@ -352,7 +368,6 @@ 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 REST_GPR(0, r1)
--
2.34.1