On Wed, Apr 20, 2022 at 03:04:14AM +0000, Tong Tiangen wrote:
> During the processing of arm64 kernel hardware memory errors(do_sea()), if
> the errors is consumed in the kernel, the current processing is panic.
> However, it is not optimal.
>
> Take uaccess for example, if the uaccess operation fails due to memory
> error, only the user process will be affected, kill the user process
> and isolate the user page with hardware memory errors is a better choice.
Conceptually, I'm fine with the idea of constraining what we do for a
true uaccess, but I don't like the implementation of this at all, and I
think we first need to clean up the arm64 extable usage to clearly
distinguish a uaccess from another access.
> This patch only enable machine error check framework, it add exception
> fixup before kernel panic in do_sea() and only limit the consumption of
> hardware memory errors in kernel mode triggered by user mode processes.
> If fixup successful, panic can be avoided.
>
> Consistent with PPC/x86, it is implemented by CONFIG_ARCH_HAS_COPY_MC.
>
> Also add copy_mc_to_user() in include/linux/uaccess.h, this helper is
> called when CONFIG_ARCH_HAS_COPOY_MC is open.
>
> Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/extable.h | 1 +
> arch/arm64/mm/extable.c | 17 +++++++++++++++++
> arch/arm64/mm/fault.c | 27 ++++++++++++++++++++++++++-
> include/linux/uaccess.h | 9 +++++++++
> 5 files changed, 54 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index d9325dd95eba..012e38309955 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -19,6 +19,7 @@ config ARM64
> select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
> select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
> select ARCH_HAS_CACHE_LINE_SIZE
> + select ARCH_HAS_COPY_MC if ACPI_APEI_GHES
> select ARCH_HAS_CURRENT_STACK_POINTER
> select ARCH_HAS_DEBUG_VIRTUAL
> select ARCH_HAS_DEBUG_VM_PGTABLE
> diff --git a/arch/arm64/include/asm/extable.h b/arch/arm64/include/asm/extable.h
> index 72b0e71cc3de..f80ebd0addfd 100644
> --- a/arch/arm64/include/asm/extable.h
> +++ b/arch/arm64/include/asm/extable.h
> @@ -46,4 +46,5 @@ bool ex_handler_bpf(const struct exception_table_entry *ex,
> #endif /* !CONFIG_BPF_JIT */
>
> bool fixup_exception(struct pt_regs *regs);
> +bool fixup_exception_mc(struct pt_regs *regs);
> #endif
> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> index 489455309695..4f0083a550d4 100644
> --- a/arch/arm64/mm/extable.c
> +++ b/arch/arm64/mm/extable.c
> @@ -9,6 +9,7 @@
>
> #include <asm/asm-extable.h>
> #include <asm/ptrace.h>
> +#include <asm/esr.h>
>
> static inline unsigned long
> get_ex_fixup(const struct exception_table_entry *ex)
> @@ -84,3 +85,19 @@ bool fixup_exception(struct pt_regs *regs)
>
> BUG();
> }
> +
> +bool fixup_exception_mc(struct pt_regs *regs)
> +{
> + const struct exception_table_entry *ex;
> +
> + ex = search_exception_tables(instruction_pointer(regs));
> + if (!ex)
> + return false;
> +
> + /*
> + * This is not complete, More Machine check safe extable type can
> + * be processed here.
> + */
> +
> + return false;
> +}
This is at best misnamed; It doesn't actually apply the fixup, it just
searches for one.
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 77341b160aca..a9e6fb1999d1 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -695,6 +695,29 @@ static int do_bad(unsigned long far, unsigned int esr, struct pt_regs *regs)
> return 1; /* "fault" */
> }
>
> +static bool arm64_do_kernel_sea(unsigned long addr, unsigned int esr,
> + struct pt_regs *regs, int sig, int code)
> +{
> + if (!IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC))
> + return false;
> +
> + if (user_mode(regs) || !current->mm)
> + return false;
> +
> + if (apei_claim_sea(regs) < 0)
> + return false;
> +
> + if (!fixup_exception_mc(regs))
> + return false;
> +
> + set_thread_esr(0, esr);
> +
> + arm64_force_sig_fault(sig, code, addr,
> + "Uncorrected hardware memory error in kernel-access\n");
> +
> + return true;
> +}
> +
> static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs)
> {
> const struct fault_info *inf;
> @@ -720,7 +743,9 @@ static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs)
> */
> siaddr = untagged_addr(far);
> }
> - arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr);
> +
> + if (!arm64_do_kernel_sea(siaddr, esr, regs, inf->sig, inf->code))
> + arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr);
>
> return 0;
> }
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 546179418ffa..884661b29c17 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -174,6 +174,15 @@ copy_mc_to_kernel(void *dst, const void *src, size_t cnt)
> }
> #endif
>
> +#ifndef copy_mc_to_user
> +static inline unsigned long __must_check
> +copy_mc_to_user(void *dst, const void *src, size_t cnt)
> +{
> + check_object_size(src, cnt, true);
> + return raw_copy_to_user(dst, src, cnt);
> +}
> +#endif
Why do we need a special copy_mc_to_user() ?
Why are we not making *every* true uaccess recoverable? That way the
regular copy_to_user() would just work.
Thanks,
Mark.
