Re: [PATCH v2 11/14] powerpc/64s: Clear/restore caller gprs in syscall interrupt/return
From: Andrew Donnellan <hidden>
Date: 2022-08-11 10:12:23
On Mon, 2022-07-25 at 16:31 +1000, Rohan McLure wrote:
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. One function of syscall_exit_prepare is to determine when non- volatile regs must be restored, and it still serves that purpose on 32-bit. Use it now for determining where to find XER, CTR, CR.
I'm not sure exactly how syscall_exit_prepare comes into this?
quoted hunk ↗ jump to hunk
Signed-off-by: Rohan McLure <redacted> --- V1 -> V2: Update summary --- arch/powerpc/kernel/interrupt_64.S | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-)diff --git a/arch/powerpc/kernel/interrupt_64.Sb/arch/powerpc/kernel/interrupt_64.S index 3e8a811e09c4..34167cfa5d60 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)@@ -108,6 +108,13 @@ 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. + */ + NULLIFY_GPRS(5, 12) + NULLIFY_NVGPRS() + /* Calling convention has r3 = orig r0, r4 = regs */ mr r3,r0 bl system_call_exception@@ -138,6 +145,7 @@ BEGIN_FTR_SECTIONHMT_MEDIUM_LOW END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) + REST_NVGPRS(r1) cmpdi r3,0 bne .Lsyscall_vectored_\name\()_restore_regs@@ -180,7 +188,6 @@ 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@@ -248,7 +255,7 @@ END_BTB_FLUSH_SECTIONld 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)@@ -298,6 +305,13 @@ END_BTB_FLUSH_SECTIONwrteei 1 #endif + /* + * Zero user registers to prevent influencing speculative execution + * state of kernel code. + */ + NULLIFY_GPRS(5, 12) + NULLIFY_NVGPRS() + /* Calling convention has r3 = orig r0, r4 = regs */ mr r3,r0 bl system_call_exception@@ -340,6 +354,7 @@ BEGIN_FTR_SECTIONstdcx. 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 */@@ -367,7 +382,6 @@ 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)
-- Andrew Donnellan OzLabs, ADL Canberra ajd@linux.ibm.com IBM Australia Limited