On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:
> Use the convenience macros for saving/clearing/restoring gprs in keeping
> with syscall calling conventions. The plural variants of these macros
> can store a range of registers for concision.
>
> This works well when the user gpr value we are hoping to save is still
> live. In the syscall interrupt handlers, user register state is
> sometimes juggled between registers. Hold-off from issuing the SAVE_GPR
> macro for applicable neighbouring lines to highlight the delicate
> register save logic.
>
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
> ---
> V1 -> V2: Update summary
> V2 -> V3: Update summary regarding exclusions for the SAVE_GPR marco.
> Acknowledge new name for ZEROIZE_GPR{,S} macros.
> ---
> arch/powerpc/kernel/interrupt_64.S | 43 ++++++----------------------
> 1 file changed, 9 insertions(+), 34 deletions(-)
>
> diff --git a/arch/powerpc/kernel/interrupt_64.S
> b/arch/powerpc/kernel/interrupt_64.S
> index a8065209dd8c..ad302ad93433 100644
> --- a/arch/powerpc/kernel/interrupt_64.S
> +++ b/arch/powerpc/kernel/interrupt_64.S
> @@ -71,12 +71,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
> mfcr r12
> li r11,0
> /* Save syscall parameters in r3-r8 */
> - std r3,GPR3(r1)
> - std r4,GPR4(r1)
> - std r5,GPR5(r1)
> - std r6,GPR6(r1)
> - std r7,GPR7(r1)
> - std r8,GPR8(r1)
> + SAVE_GPRS(3, 8, r1)
> /* Zero r9-r12, this should only be required when restoring all GPRs */
> std r11,GPR9(r1)
> std r11,GPR10(r1)
> @@ -157,17 +152,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> /* Could zero these as per ABI, but we may consider a stricter ABI
> * which preserves these if libc implementations can benefit, so
> * restore them for now until further measurement is done. */
> - ld r0,GPR0(r1)
> - ld r4,GPR4(r1)
> - ld r5,GPR5(r1)
> - ld r6,GPR6(r1)
> - ld r7,GPR7(r1)
> - ld r8,GPR8(r1)
> + REST_GPR(0, r1)
> + REST_GPRS(4, 8, r1)
> /* Zero volatile regs that may contain sensitive kernel data */
> - li r9,0
> - li r10,0
> - li r11,0
> - li r12,0
> + ZEROIZE_GPRS(9, 12)
> mtspr SPRN_XER,r0
>
> /*
> @@ -189,7 +177,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> ld r4,_LINK(r1)
> ld r5,_XER(r1)
>
> - ld r0,GPR0(r1)
> + REST_GPR(0, r1)
> mtcr r2
> mtctr r3
> mtlr r4
> @@ -257,12 +245,7 @@ END_BTB_FLUSH_SECTION
> mfcr r12
> li r11,0
> /* Save syscall parameters in r3-r8 */
> - std r3,GPR3(r1)
> - std r4,GPR4(r1)
> - std r5,GPR5(r1)
> - std r6,GPR6(r1)
> - std r7,GPR7(r1)
> - std r8,GPR8(r1)
> + SAVE_GPRS(3, 8, r1)
> /* Zero r9-r12, this should only be required when restoring all GPRs */
> std r11,GPR9(r1)
> std r11,GPR10(r1)
> @@ -360,16 +343,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
> cmpdi r3,0
> bne .Lsyscall_restore_regs
> /* Zero volatile regs that may contain sensitive kernel data */
> - li r0,0
> - li r4,0
> - li r5,0
> - li r6,0
> - li r7,0
> - li r8,0
> - li r9,0
> - li r10,0
> - li r11,0
> - li r12,0
> + ZEROIZE_GPR(0)
> + ZEROIZE_GPRS(4, 12)
> mtctr r0
> mtspr SPRN_XER,r0
> .Lsyscall_restore_regs_cont:
> @@ -394,7 +369,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> ld r4,_XER(r1)
> mtctr r3
> mtspr SPRN_XER,r4
> - ld r0,GPR0(r1)
> + REST_GPR(0, r1)
> REST_GPRS(4, 12, r1)
> b .Lsyscall_restore_regs_cont
> .Lsyscall_rst_end:
> --
> 2.34.1
