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Date: Mon, 04 Nov 2019 14:29:59 +0109
From: Marc Zyngier <maz@...nel.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas
<catalin.marinas@....com>, Steven Rostedt <rostedt@...dmis.org>, Masami
Hiramatsu <mhiramat@...nel.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Dave Martin <dave.martin@....com>, Kees Cook <keescook@...omium.org>, Laura
Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Nick
Desaulniers <ndesaulniers@...gle.com>, Jann Horn <jannh@...gle.com>, Miguel
Ojeda <miguel.ojeda.sandonis@...il.com>, Masahiro Yamada
<yamada.masahiro@...ionext.com>, <clang-built-linux@...glegroups.com>,
<kernel-hardening@...ts.openwall.com>,
<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 13/17] arm64: preserve x18 when CPU is suspended
On 2019-11-01 23:21, Sami Tolvanen wrote:
> Don't lose the current task's shadow stack when the CPU is suspended.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
> arch/arm64/include/asm/suspend.h | 2 +-
> arch/arm64/mm/proc.S | 10 ++++++++++
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/suspend.h
> b/arch/arm64/include/asm/suspend.h
> index 8939c87c4dce..0cde2f473971 100644
> --- a/arch/arm64/include/asm/suspend.h
> +++ b/arch/arm64/include/asm/suspend.h
> @@ -2,7 +2,7 @@
> #ifndef __ASM_SUSPEND_H
> #define __ASM_SUSPEND_H
>
> -#define NR_CTX_REGS 12
> +#define NR_CTX_REGS 13
> #define NR_CALLEE_SAVED_REGS 12
>
> /*
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index fdabf40a83c8..5616dc52a033 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -49,6 +49,8 @@
> * cpu_do_suspend - save CPU registers context
> *
> * x0: virtual address of context pointer
> + *
> + * This must be kept in sync with struct cpu_suspend_ctx in
> <asm/suspend.h>.
> */
> ENTRY(cpu_do_suspend)
> mrs x2, tpidr_el0
> @@ -73,6 +75,9 @@ alternative_endif
> stp x8, x9, [x0, #48]
> stp x10, x11, [x0, #64]
> stp x12, x13, [x0, #80]
> +#ifdef CONFIG_SHADOW_CALL_STACK
> + str x18, [x0, #96]
> +#endif
Do we need the #ifdefery here? We didn't add that to the KVM path,
and I'd feel better having a single behaviour, specially when
NR_CTX_REGS is unconditionally sized to hold 13 regs.
> ret
> ENDPROC(cpu_do_suspend)
>
> @@ -89,6 +94,11 @@ ENTRY(cpu_do_resume)
> ldp x9, x10, [x0, #48]
> ldp x11, x12, [x0, #64]
> ldp x13, x14, [x0, #80]
> +#ifdef CONFIG_SHADOW_CALL_STACK
> + ldr x18, [x0, #96]
> + /* Clear the SCS pointer from the state buffer */
> + str xzr, [x0, #96]
> +#endif
> msr tpidr_el0, x2
> msr tpidrro_el0, x3
> msr contextidr_el1, x4
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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