[PATCH v2 14/14] powerpc/64s: Clear gprs on interrupt routine entry
Andrew Donnellan
ajd at linux.ibm.com
Fri Aug 12 18:26:58 AEST 2022
On Mon, 2022-07-25 at 16:32 +1000, Rohan McLure wrote:
> Zero GPRS r0, r2-r11, r14-r31, on entry into the kernel for all
> other interrupt sources to limit influence of user-space values
> in potential speculation gadgets. The remaining gprs are overwritten
> by
> entry macros to interrupt handlers, irrespective of whether or not a
> given handler consumes these register values.
>
> Prior to this commit, r14-r31 are restored on a per-interrupt basis
> at
> exit, but now they are always restored. Remove explicit REST_NVGPRS
> invocations on interrupt entry and simplify exit logic. 32-bit
I wouldn't describe the existing uses of REST_NVGPRS as "on interrupt
entry" given they all happen right before branching to
interrupt_return_srr.
> systems
> will still conditionally need to restore NVGPRS so keep return value
> for
> interrupt_exit_user_prepare.
Could you clarify what you mean here?
>
> 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.
>
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> ---
> V1 -> V2: Add benchmark data
> ---
> arch/powerpc/kernel/exceptions-64s.S | 21 ++++++++-------------
> arch/powerpc/kernel/interrupt_64.S | 9 ++-------
> 2 files changed, 10 insertions(+), 20 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S
> b/arch/powerpc/kernel/exceptions-64s.S
> index 102896fc6a86..62dd6270852e 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -502,6 +502,7 @@ 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 */
> + NULLIFY_GPR(0)
>
> /* Mark our [H]SRRs valid for return */
> li r10,1
> @@ -538,14 +539,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> ld r10,IAREA+EX_R10(r13)
> std r9,GPR9(r1)
> std r10,GPR10(r1)
> + NULLIFY_GPRS(9, 10)
> ld r9,IAREA+EX_R11(r13) /* move r11 - r13 to
> stackframe */
> ld r10,IAREA+EX_R12(r13)
> ld r11,IAREA+EX_R13(r13)
> std r9,GPR11(r1)
> std r10,GPR12(r1)
> std r11,GPR13(r1)
> + /* keep r12 ([H]SRR1/MSR), r13 (PACA) for interrupt routine
> */
> + NULLIFY_GPR(11)
>
> SAVE_NVGPRS(r1)
> + NULLIFY_NVGPRS()
>
> .if IDAR
> .if IISIDE
> @@ -577,8 +582,8 @@ 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 */
> + NULLIFY_GPRS(2, 8)
> mflr r9 /* Get LR, later save to
> stack */
> ld r2,PACATOC(r13) /* get kernel TOC into
> r2 */
> std r9,_LINK(r1)
> @@ -696,6 +701,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
> mtlr r9
> ld r9,_CCR(r1)
> mtcr r9
> + REST_NVGPRS(r1)
> REST_GPRS(2, 13, r1)
> REST_GPR(0, r1)
> /* restore original r1. */
> @@ -1368,11 +1374,6 @@
> ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
> b interrupt_return_srr
>
> 1: bl do_break
> - /*
> - * 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)
> b interrupt_return_srr
>
>
> @@ -1598,7 +1599,6 @@ EXC_COMMON_BEGIN(alignment_common)
> GEN_COMMON alignment
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl alignment_exception
> - REST_NVGPRS(r1) /* instruction emulation may change GPRs */
> b interrupt_return_srr
>
>
> @@ -1708,7 +1708,6 @@ EXC_COMMON_BEGIN(program_check_common)
> .Ldo_program_check:
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl program_check_exception
> - REST_NVGPRS(r1) /* instruction emulation may change GPRs */
> b interrupt_return_srr
>
>
> @@ -2139,7 +2138,6 @@ EXC_COMMON_BEGIN(emulation_assist_common)
> GEN_COMMON emulation_assist
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl emulation_assist_interrupt
> - REST_NVGPRS(r1) /* instruction emulation may change GPRs */
> b interrupt_return_hsrr
>
>
> @@ -2457,7 +2455,6 @@ EXC_COMMON_BEGIN(facility_unavailable_common)
> GEN_COMMON facility_unavailable
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl facility_unavailable_exception
> - REST_NVGPRS(r1) /* instruction emulation may change GPRs */
> b interrupt_return_srr
>
>
> @@ -2485,7 +2482,6 @@ EXC_COMMON_BEGIN(h_facility_unavailable_common)
> GEN_COMMON h_facility_unavailable
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl facility_unavailable_exception
> - REST_NVGPRS(r1) /* XXX Shouldn't be necessary in practice */
> b interrupt_return_hsrr
>
>
> @@ -2711,7 +2707,6 @@ EXC_COMMON_BEGIN(altivec_assist_common)
> addi r3,r1,STACK_FRAME_OVERHEAD
> #ifdef CONFIG_ALTIVEC
> bl altivec_assist_exception
> - REST_NVGPRS(r1) /* instruction emulation may change GPRs */
> #else
> bl unknown_exception
> #endif
> diff --git a/arch/powerpc/kernel/interrupt_64.S
> b/arch/powerpc/kernel/interrupt_64.S
> index efaf162fa772..083a94604072 100644
> --- a/arch/powerpc/kernel/interrupt_64.S
> +++ b/arch/powerpc/kernel/interrupt_64.S
> @@ -430,9 +430,6 @@ interrupt_return_\srr\()_user: /* make backtraces
> match the _kernel variant */
> _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user)
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl interrupt_exit_user_prepare
> - cmpdi r3,0
> - bne- .Lrestore_nvgprs_\srr
> -.Lrestore_nvgprs_\srr\()_cont:
> std r1,PACA_EXIT_SAVE_R1(r13) /* save r1 for restart */
> #ifdef CONFIG_PPC_BOOK3S
> .Linterrupt_return_\srr\()_user_rst_start:
> @@ -446,6 +443,7 @@
> _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user)
> stb r11,PACAIRQHAPPENED(r13) # clear out possible
> HARD_DIS
>
> .Lfast_user_interrupt_return_\srr\():
> + REST_NVGPRS(r1)
> #ifdef CONFIG_PPC_BOOK3S
> .ifc \srr,srr
> lbz r4,PACASRR_VALID(r13)
> @@ -515,10 +513,6 @@
> ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
> b . /* prevent speculative execution */
> .Linterrupt_return_\srr\()_user_rst_end:
>
> -.Lrestore_nvgprs_\srr\():
> - REST_NVGPRS(r1)
> - b .Lrestore_nvgprs_\srr\()_cont
> -
> #ifdef CONFIG_PPC_BOOK3S
> interrupt_return_\srr\()_user_restart:
> _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user_restart)
> @@ -559,6 +553,7 @@
> _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_kernel)
> 1:
>
> .Lfast_kernel_interrupt_return_\srr\():
> + REST_NVGPRS(r1)
> cmpdi cr1,r3,0
> #ifdef CONFIG_PPC_BOOK3S
> .ifc \srr,srr
--
Andrew Donnellan OzLabs, ADL Canberra
ajd at linux.ibm.com IBM Australia Limited
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