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    Subject[PATCH v13 06/12] arm64: preserve x18 when CPU is suspended
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    Don't lose the current task's shadow stack when the CPU is suspended.

    Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: Mark Rutland <mark.rutland@arm.com>
    Acked-by: Will Deacon <will@kernel.org>
    ---
    arch/arm64/include/asm/suspend.h | 2 +-
    arch/arm64/mm/proc.S | 14 ++++++++++++++
    2 files changed, 15 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 197a9ba2d5ea..ed15be0f8103 100644
    --- a/arch/arm64/mm/proc.S
    +++ b/arch/arm64/mm/proc.S
    @@ -58,6 +58,8 @@
    * 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>.
    */
    SYM_FUNC_START(cpu_do_suspend)
    mrs x2, tpidr_el0
    @@ -82,6 +84,11 @@ alternative_endif
    stp x8, x9, [x0, #48]
    stp x10, x11, [x0, #64]
    stp x12, x13, [x0, #80]
    + /*
    + * Save x18 as it may be used as a platform register, e.g. by shadow
    + * call stack.
    + */
    + str x18, [x0, #96]
    ret
    SYM_FUNC_END(cpu_do_suspend)

    @@ -98,6 +105,13 @@ SYM_FUNC_START(cpu_do_resume)
    ldp x9, x10, [x0, #48]
    ldp x11, x12, [x0, #64]
    ldp x13, x14, [x0, #80]
    + /*
    + * Restore x18, as it may be used as a platform register, and clear
    + * the buffer to minimize the risk of exposure when used for shadow
    + * call stack.
    + */
    + ldr x18, [x0, #96]
    + str xzr, [x0, #96]
    msr tpidr_el0, x2
    msr tpidrro_el0, x3
    msr contextidr_el1, x4
    --
    2.26.2.303.gf8c07b1a785-goog
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