在 2024/8/20 17:12, Mark Rutland 写道:
On Tue, Aug 20, 2024 at 10:11:45AM +0800, Tong Tiangen wrote:
在 2024/8/20 1:29, Mark Rutland 写道:
Hi Tong,
On Tue, May 28, 2024 at 04:59:11PM +0800, Tong Tiangen wrote:
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 <tongtiangen@xxxxxxxxxx>
[...]
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!
[...]
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?
Taking x86 as an example:
unsigned long __must_check copy_mc_to_user(...)
{
unsigned long ret;
if (copy_mc_fragile_enabled) {
instrument_copy_to_user(dst, src, len);
__uaccess_begin();
ret = copy_mc_fragile((__force void *)dst, src, len);
__uaccess_end();
return ret;
}
if (static_cpu_has(X86_FEATURE_ERMS)) {
instrument_copy_to_user(dst, src, len);
__uaccess_begin();
ret = copy_mc_enhanced_fast_string((__force void *)dst, src, len);
__uaccess_end();
return ret;
}
return copy_user_generic((__force void *)dst, src, len);
}
Through checking the source code, I found that "copy_mc_fragile_enabled"
and "X86_FEATURE_ERMS" both rely on the hardware features of x86. I
cannot explain the reasons for the details, but I feel that these are
related to the hardware implementation.
Dan Williams should be able to explain the reason.
Hi Dan:
We need your help:)
Compared to copy_to_user(), copy_mc_to_user() added memory error
handling. My question is why the error handling is not directly
implemented on copy_to_user(), but instead the copy_mc_to_user()
function is added? Related to hardware features or performance
considerations ?
Thanks,
Tong.
[...]
+/*
+ * 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.
I roughly understand what you mean. The prerequisite of fixup is sea
claimed succeed. But the fixup here actually just set the regs->pc, and
not applied the fixup handler here. If claim sea fails, it will directly
panic() here without applying the fixup handler.
Thanks,
Tong.
.
