Le 19/08/2022 à 05:38, Rohan McLure a écrit : > 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 > --- > 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..d9625113c7a5 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. > + */ > + NULLIFY_GPRS(5, 12)
Macro name has changed. > + NULLIFY_NVGPRS() Why clearing non volatile GPRs ? They are supposed to be callee saved so I can't see how they could be used for speculation. Do you have any exemple ? > + > /* 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) What is the link between this change and the description in the commit message ? > 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. > + */ > + NULLIFY_GPRS(5, 12) > + NULLIFY_NVGPRS() > + Name has changed. > /* 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) Same question. > 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)
