On Wed, Apr 20, 2022 at 03:04:17AM +0000, Tong Tiangen wrote:
> Add {get, put}_user() to machine check safe.
>
> If get/put fail due to hardware memory error, only the relevant processes
> are affected, so killing the user process and isolate the user page with
> hardware memory errors is a more reasonable choice than kernel panic.
>
> Add new extable type EX_TYPE_UACCESS_MC_ERR_ZERO which can be used for
> uaccess that can be recovered from hardware memory errors. The difference
> from EX_TYPE_UACCESS_MC is that this type also sets additional two target
> register which save error code and value needs to be set zero.
Why does this need to be in any way distinct from the existing
EX_TYPE_UACCESS_ERR_ZERO ?
Other than the case where we currently (ab)use that for
copy_{to,from}_kernel_nofault(), where do we *not* want to use
EX_TYPE_UACCESS_ERR_ZERO and *not* recover from a memory error?
Thanks,
Mark.
>
> Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/asm-extable.h | 14 ++++++++++++++
> arch/arm64/include/asm/uaccess.h | 4 ++--
> arch/arm64/mm/extable.c | 4 ++++
> 3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
> index 75b2c00e9523..80410899a9ad 100644
> --- a/arch/arm64/include/asm/asm-extable.h
> +++ b/arch/arm64/include/asm/asm-extable.h
> @@ -13,6 +13,7 @@
>
> /* _MC indicates that can fixup from machine check errors */
> #define EX_TYPE_UACCESS_MC 5
> +#define EX_TYPE_UACCESS_MC_ERR_ZERO 6
>
> #ifdef __ASSEMBLY__
>
> @@ -78,6 +79,15 @@
> #define EX_DATA_REG(reg, gpr) \
> "((.L__gpr_num_" #gpr ") << " __stringify(EX_DATA_REG_##reg##_SHIFT) ")"
>
> +#define _ASM_EXTABLE_UACCESS_MC_ERR_ZERO(insn, fixup, err, zero) \
> + __DEFINE_ASM_GPR_NUMS \
> + __ASM_EXTABLE_RAW(#insn, #fixup, \
> + __stringify(EX_TYPE_UACCESS_MC_ERR_ZERO), \
> + "(" \
> + EX_DATA_REG(ERR, err) " | " \
> + EX_DATA_REG(ZERO, zero) \
> + ")")
> +
> #define _ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, zero) \
> __DEFINE_ASM_GPR_NUMS \
> __ASM_EXTABLE_RAW(#insn, #fixup, \
> @@ -90,6 +100,10 @@
> #define _ASM_EXTABLE_UACCESS_ERR(insn, fixup, err) \
> _ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, wzr)
>
> +
> +#define _ASM_EXTABLE_UACCESS_MC_ERR(insn, fixup, err) \
> + _ASM_EXTABLE_UACCESS_MC_ERR_ZERO(insn, fixup, err, wzr)
> +
> #define EX_DATA_REG_DATA_SHIFT 0
> #define EX_DATA_REG_DATA GENMASK(4, 0)
> #define EX_DATA_REG_ADDR_SHIFT 5
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index e8dce0cc5eaa..e41b47df48b0 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -236,7 +236,7 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
> asm volatile( \
> "1: " load " " reg "1, [%2]\n" \
> "2:\n" \
> - _ASM_EXTABLE_UACCESS_ERR_ZERO(1b, 2b, %w0, %w1) \
> + _ASM_EXTABLE_UACCESS_MC_ERR_ZERO(1b, 2b, %w0, %w1) \
> : "+r" (err), "=&r" (x) \
> : "r" (addr))
>
> @@ -325,7 +325,7 @@ do { \
> asm volatile( \
> "1: " store " " reg "1, [%2]\n" \
> "2:\n" \
> - _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w0) \
> + _ASM_EXTABLE_UACCESS_MC_ERR(1b, 2b, %w0) \
> : "+r" (err) \
> : "r" (x), "r" (addr))
>
> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> index 525876c3ebf4..1023ccdb2f89 100644
> --- a/arch/arm64/mm/extable.c
> +++ b/arch/arm64/mm/extable.c
> @@ -88,6 +88,7 @@ bool fixup_exception(struct pt_regs *regs)
> case EX_TYPE_BPF:
> return ex_handler_bpf(ex, regs);
> case EX_TYPE_UACCESS_ERR_ZERO:
> + case EX_TYPE_UACCESS_MC_ERR_ZERO:
> return ex_handler_uaccess_err_zero(ex, regs);
> case EX_TYPE_LOAD_UNALIGNED_ZEROPAD:
> return ex_handler_load_unaligned_zeropad(ex, regs);
> @@ -107,6 +108,9 @@ bool fixup_exception_mc(struct pt_regs *regs)
> switch (ex->type) {
> case EX_TYPE_UACCESS_MC:
> return ex_handler_uaccess_type(ex, regs, FIXUP_TYPE_MC);
> + case EX_TYPE_UACCESS_MC_ERR_ZERO:
> + return ex_handler_uaccess_err_zero(ex, regs);
> +
> }
>
> return false;
> --
> 2.25.1
>
