powerpc/64s: Zeroise gprs on interrupt routine entry on Book3S

Zeroise 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.

Zeroise GPRS r0, r2-r11, r14-r31, on entry into the kernel for all
other interrupt sources. The remaining gprs are overwritten by
entry macros to interrupt handlers, irrespective of whether or not a
given handler consumes these register values. If an interrupt does not
select the IMSR_R12 IOption, zeroise r12.

Prior to this commit, r14-r31 are restored on a per-interrupt basis at
exit, but now they are always restored on 64bit Book3S. Remove explicit
REST_NVGPRS invocations on 64-bit Book3S. 32-bit systems do not clear
user registers on interrupt, and continue to depend on the return value
of interrupt_exit_user_prepare to determine whether or not to restore
non-volatiles.

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. This mitigation is able to be enabled/disabled through
CONFIG_INTERRUPT_SANITIZE_REGISTERS.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221201071019.1953023-5-rmclure@linux.ibm.com
This commit is contained in:
Rohan McLure 2022-12-01 18:10:17 +11:00 committed by Michael Ellerman
parent 2487fd2e6d
commit 1df45d78b8
2 changed files with 32 additions and 11 deletions

View File

@ -506,6 +506,7 @@ 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 */
SANITIZE_GPR(0)
/* Mark our [H]SRRs valid for return */
li r10,1
@ -548,8 +549,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
std r9,GPR11(r1)
std r10,GPR12(r1)
std r11,GPR13(r1)
.if !IMSR_R12
SANITIZE_GPRS(9, 12)
.else
SANITIZE_GPRS(9, 11)
.endif
SAVE_NVGPRS(r1)
SANITIZE_NVGPRS()
.if IDAR
.if IISIDE
@ -581,8 +588,8 @@ 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 */
SANITIZE_GPRS(2, 8)
mflr r9 /* Get LR, later save to stack */
LOAD_PACA_TOC() /* get kernel TOC into r2 */
std r9,_LINK(r1)
@ -700,6 +707,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
mtlr r9
ld r9,_CCR(r1)
mtcr r9
SANITIZE_RESTORE_NVGPRS()
REST_GPRS(2, 13, r1)
REST_GPR(0, r1)
/* restore original r1. */
@ -1445,7 +1453,7 @@ ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
* 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)
HANDLER_RESTORE_NVGPRS()
b interrupt_return_srr
@ -1671,7 +1679,7 @@ EXC_COMMON_BEGIN(alignment_common)
GEN_COMMON alignment
addi r3,r1,STACK_INT_FRAME_REGS
bl alignment_exception
REST_NVGPRS(r1) /* instruction emulation may change GPRs */
HANDLER_RESTORE_NVGPRS() /* instruction emulation may change GPRs */
b interrupt_return_srr
@ -1737,7 +1745,7 @@ EXC_COMMON_BEGIN(program_check_common)
.Ldo_program_check:
addi r3,r1,STACK_INT_FRAME_REGS
bl program_check_exception
REST_NVGPRS(r1) /* instruction emulation may change GPRs */
HANDLER_RESTORE_NVGPRS() /* instruction emulation may change GPRs */
b interrupt_return_srr
@ -2169,7 +2177,7 @@ EXC_COMMON_BEGIN(emulation_assist_common)
GEN_COMMON emulation_assist
addi r3,r1,STACK_INT_FRAME_REGS
bl emulation_assist_interrupt
REST_NVGPRS(r1) /* instruction emulation may change GPRs */
HANDLER_RESTORE_NVGPRS() /* instruction emulation may change GPRs */
b interrupt_return_hsrr
@ -2501,7 +2509,7 @@ EXC_COMMON_BEGIN(facility_unavailable_common)
GEN_COMMON facility_unavailable
addi r3,r1,STACK_INT_FRAME_REGS
bl facility_unavailable_exception
REST_NVGPRS(r1) /* instruction emulation may change GPRs */
HANDLER_RESTORE_NVGPRS() /* instruction emulation may change GPRs */
b interrupt_return_srr
@ -2529,7 +2537,8 @@ EXC_COMMON_BEGIN(h_facility_unavailable_common)
GEN_COMMON h_facility_unavailable
addi r3,r1,STACK_INT_FRAME_REGS
bl facility_unavailable_exception
REST_NVGPRS(r1) /* XXX Shouldn't be necessary in practice */
/* XXX Shouldn't be necessary in practice */
HANDLER_RESTORE_NVGPRS()
b interrupt_return_hsrr
@ -2755,7 +2764,7 @@ EXC_COMMON_BEGIN(altivec_assist_common)
addi r3,r1,STACK_INT_FRAME_REGS
#ifdef CONFIG_ALTIVEC
bl altivec_assist_exception
REST_NVGPRS(r1) /* instruction emulation may change GPRs */
HANDLER_RESTORE_NVGPRS() /* instruction emulation may change GPRs */
#else
bl unknown_exception
#endif

View File

@ -96,6 +96,11 @@ 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.
*/
SANITIZE_SYSCALL_GPRS()
bl system_call_exception
.Lsyscall_vectored_\name\()_exit:
@ -124,6 +129,7 @@ BEGIN_FTR_SECTION
HMT_MEDIUM_LOW
END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
SANITIZE_RESTORE_NVGPRS()
cmpdi r3,0
bne .Lsyscall_vectored_\name\()_restore_regs
@ -159,7 +165,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
ld r4,_LINK(r1)
ld r5,_XER(r1)
REST_NVGPRS(r1)
HANDLER_RESTORE_NVGPRS()
REST_GPR(0, r1)
mtcr r2
mtctr r3
@ -275,6 +281,11 @@ END_BTB_FLUSH_SECTION
wrteei 1
#endif
/*
* Zero user registers to prevent influencing speculative execution
* state of kernel code.
*/
SANITIZE_SYSCALL_GPRS()
bl system_call_exception
.Lsyscall_exit:
@ -315,6 +326,7 @@ BEGIN_FTR_SECTION
stdcx. r0,0,r1 /* to clear the reservation */
END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
SANITIZE_RESTORE_NVGPRS()
cmpdi r3,0
bne .Lsyscall_restore_regs
/* Zero volatile regs that may contain sensitive kernel data */
@ -342,7 +354,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
.Lsyscall_restore_regs:
ld r3,_CTR(r1)
ld r4,_XER(r1)
REST_NVGPRS(r1)
HANDLER_RESTORE_NVGPRS()
mtctr r3
mtspr SPRN_XER,r4
REST_GPR(0, r1)