在 2022/5/13 23:26, Mark Rutland 写道:
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.
OK,using EX_TYPE_UACCESS and this extable type could be recover, this is more reasonable.
For EX_TYPE_UACCESS_ERR_ZERO, today we use it for kernel accesses in a couple of cases, such as get_user/futex/__user_cache_maint()/__user_swpX_asm(), your suggestion is: get_user continues to use EX_TYPE_UACCESS_ERR_ZERO and the other cases use new type EX_TYPE_FIXUP_ERR_ZERO?
Thanks, Tong.
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 longget_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.
Yeah, you're right about the current logic, so i added notes to explain the scenarios that will be added later.
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); +} +#endifWhy 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.
Agreed, will fixed next version. Thanks, Tong.
Thanks, Mark. .
