Re: [PATCH -next v5 7/8] arm64: add uaccess to machine check safe
From: Mark Rutland <mark.rutland@arm.com>
Date: 2022-06-17 09:07:12
Also in:
linux-arm-kernel, linux-mm, lkml
On Sat, May 28, 2022 at 06:50:55AM +0000, Tong Tiangen wrote:
If user access fail due to hardware memory error, only the relevant processes are affected, so killing the user process and isolate the error page with hardware memory errors is a more reasonable choice than kernel panic. Signed-off-by: Tong Tiangen <redacted>
--- arch/arm64/lib/copy_from_user.S | 8 ++++---- arch/arm64/lib/copy_to_user.S | 8 ++++----
All of these changes are to the *kernel* accesses performed as part of copy to/from user, and have nothing to do with userspace, so it does not make sense to mark these as UACCESS. Do we *actually* need to recover from failues on these accesses? Looking at _copy_from_user(), the kernel will immediately follow this up with a memset() to the same address which will be fatal anyway, so this is only punting the failure for a few instructions. If we really need to recover from certain accesses to kernel memory we should add a new EX_TYPE_KACCESS_ERR_ZERO_MC or similar, but we need a strong rationale as to why that's useful. As things stand I do not beleive it makes sense for copy to/from user specifically.
quoted hunk ↗ jump to hunk
arch/arm64/mm/extable.c | 8 ++++---- 3 files changed, 12 insertions(+), 12 deletions(-)diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S index 34e317907524..402dd48a4f93 100644 --- a/arch/arm64/lib/copy_from_user.S +++ b/arch/arm64/lib/copy_from_user.S@@ -25,7 +25,7 @@ .endm .macro strb1 reg, ptr, val - strb \reg, [\ptr], \val + USER(9998f, strb \reg, [\ptr], \val) .endm .macro ldrh1 reg, ptr, val@@ -33,7 +33,7 @@ .endm .macro strh1 reg, ptr, val - strh \reg, [\ptr], \val + USER(9998f, strh \reg, [\ptr], \val) .endm .macro ldr1 reg, ptr, val@@ -41,7 +41,7 @@ .endm .macro str1 reg, ptr, val - str \reg, [\ptr], \val + USER(9998f, str \reg, [\ptr], \val) .endm .macro ldp1 reg1, reg2, ptr, val@@ -49,7 +49,7 @@ .endm .macro stp1 reg1, reg2, ptr, val - stp \reg1, \reg2, [\ptr], \val + USER(9998f, stp \reg1, \reg2, [\ptr], \val) .endm end .req x5diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S index 802231772608..4134bdb3a8b0 100644 --- a/arch/arm64/lib/copy_to_user.S +++ b/arch/arm64/lib/copy_to_user.S@@ -20,7 +20,7 @@ * x0 - bytes not copied */ .macro ldrb1 reg, ptr, val - ldrb \reg, [\ptr], \val + USER(9998f, ldrb \reg, [\ptr], \val) .endm .macro strb1 reg, ptr, val@@ -28,7 +28,7 @@ .endm .macro ldrh1 reg, ptr, val - ldrh \reg, [\ptr], \val + USER(9998f, ldrh \reg, [\ptr], \val) .endm .macro strh1 reg, ptr, val@@ -36,7 +36,7 @@ .endm .macro ldr1 reg, ptr, val - ldr \reg, [\ptr], \val + USER(9998f, ldr \reg, [\ptr], \val) .endm .macro str1 reg, ptr, val@@ -44,7 +44,7 @@ .endm .macro ldp1 reg1, reg2, ptr, val - ldp \reg1, \reg2, [\ptr], \val + USER(9998f, ldp \reg1, \reg2, [\ptr], \val) .endm .macro stp1 reg1, reg2, ptr, valdiff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c index c301dcf6335f..8ca8d9639f9f 100644 --- a/arch/arm64/mm/extable.c +++ b/arch/arm64/mm/extable.c@@ -86,10 +86,10 @@ bool fixup_exception_mc(struct pt_regs *regs) if (!ex) return false; - /* - * This is not complete, More Machine check safe extable type can - * be processed here. - */ + switch (ex->type) { + case EX_TYPE_UACCESS_ERR_ZERO: + return ex_handler_uaccess_err_zero(ex, regs); + }
This addition specifically makes sense to me, so can you split this into a separate patch? Thanks, Mark.