Re: [PATCH -next v4 6/7] arm64: add {get, put}_user to machine check safe

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在 2022/5/13 23:39, Mark Rutland 写道:
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.

There are some cases (futex/__user_cache_maint()/__user_swpX_asm()) using EX_TYPE_UACCESS_ERR_ZERO, for these cases, whether to restore is not yet determined, let's discuss in patch 3/7.

Thanks,
Tong.



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

.




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