On Tue, Aug 20, 2024 at 10:11:45AM +0800, Tong Tiangen wrote:

在 2024/8/20 1:29, Mark Rutland 写道:

quoted

Hi Tong,

On Tue, May 28, 2024 at 04:59:11PM +0800, Tong Tiangen wrote:

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For the arm64 kernel, when it processes hardware memory errors for
synchronize notifications(do_sea()), if the errors is consumed within the
kernel, the current processing is panic. However, it is not optimal.

Take copy_from/to_user for example, If ld* triggers a memory error, even in
kernel mode, only the associated process is affected. Killing the user
process and isolating the corrupt page is a better choice.

New fixup type EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE is added to identify insn
that can recover from memory errors triggered by access to kernel memory.

Signed-off-by: Tong Tiangen <redacted>

[...]

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diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
index 980d1dd8e1a3..9c0664fe1eb1 100644
--- a/arch/arm64/include/asm/asm-extable.h
+++ b/arch/arm64/include/asm/asm-extable.h

@@ -5,11 +5,13 @@
  #include <linux/bits.h>
  #include <asm/gpr-num.h>
-#define EX_TYPE_NONE			0
-#define EX_TYPE_BPF			1
-#define EX_TYPE_UACCESS_ERR_ZERO	2
-#define EX_TYPE_KACCESS_ERR_ZERO	3
-#define EX_TYPE_LOAD_UNALIGNED_ZEROPAD	4
+#define EX_TYPE_NONE				0
+#define EX_TYPE_BPF				1
+#define EX_TYPE_UACCESS_ERR_ZERO		2
+#define EX_TYPE_KACCESS_ERR_ZERO		3
+#define EX_TYPE_LOAD_UNALIGNED_ZEROPAD		4
+/* kernel access memory error safe */
+#define EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE	5

Could we please use 'MEM_ERR', and likewise for the macros below? That's
more obvious than 'ME_SAFE', and we wouldn't need the comment here.
Likewise elsewhere in this patch and the series.

To Jonathan's comment, I do prefer these numbers are aligned, so aside
from the naming, the diff above looks good.

OK, I also modified other locations to use 'MEM_ERR'.

Thanks!

[...]

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diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 802231772608..2ac716c0d6d8 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
+	KERNEL_ME_SAFE(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
+	KERNEL_ME_SAFE(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
+	KERNEL_ME_SAFE(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
+	KERNEL_ME_SAFE(9998f, ldp \reg1, \reg2, [\ptr], \val)
  	.endm
  	.macro stp1 reg1, reg2, ptr, val

These changes mean that regular copy_to_user() will handle kernel memory
errors, rather than only doing that in copy_mc_to_user(). If that's
intentional, please call that out explicitly in the commit message.

Yes. This is the purpose of the modification. If the copy_to_user()
function encounters a memory error, this uaccess affects only the
current process. and only need to kill the current process instead of
the entire kernel panic. Do not add copy_mc_to_user() so that
copy_to_user() can process memory errors.

I'll add a description in the commit msg next version.

Ok; why do powerpc and x86 have separate copy_mc_to_user()
implementations, then?

[...]

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+/*
+ * APEI claimed this as a firmware-first notification.
+ * Some processing deferred to task_work before ret_to_user().
+ */
+static bool do_apei_claim_sea(struct pt_regs *regs)
+{
+	if (user_mode(regs)) {
+		if (!apei_claim_sea(regs))
+			return true;
+	} else if (IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) {
+		if (fixup_exception_me(regs) && !apei_claim_sea(regs))
+			return true;
+	}
+
+	return false;
+}

Hmm... that'll fixup the exception even if we don't manage to claim a
the SEA. I suspect this should probably be:

static bool do_apei_claim_sea(struct pt_regs *regs)
{
	if (apei_claim_sea(regs))
		return false;
	if (user_mode(regs))
		return true;
	if (IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC))
		return !fixup_excepton_mem_err(regs);
	
	return false;
}

... unless we *don't* want to claim the SEA in the case we don't have a
fixup?

Mark.

Yes. My original meaning here is that if not have fixup, panic is
performed in do_sea() according to the original logic, and claim sea is
not required.

AFAICT my suggestion doesn't change that; if we don't have a fixup the
proprosed do_apei_claim_sea() would return false, and so do_sea() would
caryy on to arm64_notify_die(...).

I'm specifically asking if we need to avoid calling apei_claim_sea()
when we don't have a fixup handler, or if calling that would be fine.

One important thing is that if apei_claim_sea() fails to claim the SEA,
we'd like to panic(), and in that case it'd be good to have not applied
the fixup handler, so that the pt_regs::pc shows where the fault was
taken from.

Mark.