From: Borislav Petkov <bp@alien8.de>
To: Tony Luck <tony.luck@intel.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Andy Lutomirski" <luto@kernel.org>,
"Aili Yao" <yaoaili@kingsoft.com>,
"HORIGUCHI NAOYA( 堀口 直也)" <naoya.horiguchi@nec.com>
Subject: Re: [PATCH 1/4] x86/mce: Fix copyin code to return -EFAULT on machine check.
Date: Tue, 6 Apr 2021 21:24:46 +0200 [thread overview]
Message-ID: <20210406192446.GP17806@zn.tnic> (raw)
In-Reply-To: <20210326000235.370514-2-tony.luck@intel.com>
On Thu, Mar 25, 2021 at 05:02:32PM -0700, Tony Luck wrote:
> When copy from user fails due to a machine check on poison reading
> user data it should return an error code.
>
> ---
>
> Separate patch just now, but likely needs to be combined with patches
> to iteration code for bisection safety.
> ---
> arch/x86/lib/copy_user_64.S | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
> index 77b9b2a3b5c8..2987118c541a 100644
> --- a/arch/x86/lib/copy_user_64.S
> +++ b/arch/x86/lib/copy_user_64.S
> @@ -14,6 +14,7 @@
> #include <asm/alternative-asm.h>
> #include <asm/asm.h>
> #include <asm/smap.h>
> +#include <asm/errno.h>
> #include <asm/export.h>
> #include <asm/trapnr.h>
>
> @@ -237,18 +238,21 @@ SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
> cmp $X86_TRAP_MC,%eax /* check if X86_TRAP_MC */
> je 3f
> 1: rep movsb
> -2: mov %ecx,%eax
> + mov %ecx,%eax
> + ASM_CLAC
> + ret
> +
> +2:
> + cmp $X86_TRAP_MC,%eax
> + je 3f
> + mov %ecx,%eax
> ASM_CLAC
> ret
>
> /*
> - * Return zero to pretend that this copy succeeded. This
> - * is counter-intuitive, but needed to prevent the code
> - * in lib/iov_iter.c from retrying and running back into
> - * the poison cache line again. The machine check handler
> - * will ensure that a SIGBUS is sent to the task.
> + * Return -EFAULT for the machine check cases
> */
> -3: xorl %eax,%eax
> +3: movl $-EFAULT,%eax
> ASM_CLAC
> ret
Right, looks ok after swapping all that
fault-handlers-rerouting-based-on-labels thing back in. You'd need to
update the blubber in the comment above it that we're returning -EFAULT
now too.
Also, you might wanna converge the exit paths to a single "out" label
if the unconditional JMPs are not that big of a deal (pasting the whole
thing and not as a diff because diff is unreadable):
SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
movl %edx,%ecx
cmp $X86_TRAP_MC,%eax /* check if X86_TRAP_MC */
je 3f
1: rep movsb
mov %ecx,%eax
jmp out
2: cmp $X86_TRAP_MC,%eax
je 3f
mov %ecx,%eax
jmp out
/* Return -EFAULT for the machine check cases */
3: movl $-EFAULT,%eax
out:
ASM_CLAC
ret
_ASM_EXTABLE_CPY(1b, 2b)
SYM_CODE_END(.Lcopy_user_handle_tail)
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-04-06 19:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-26 0:02 [RFC 0/4] Fix machine check recovery for copy_from_user Tony Luck
2021-03-26 0:02 ` [PATCH 1/4] x86/mce: Fix copyin code to return -EFAULT on machine check Tony Luck
2021-04-06 19:24 ` Borislav Petkov [this message]
2021-03-26 0:02 ` [PATCH 2/4] mce/iter: Check for copyin failure & return error up stack Tony Luck
2021-03-26 0:02 ` [PATCH 3/4] mce/copyin: fix to not SIGBUS when copying from user hits poison Tony Luck
2021-04-07 21:18 ` Borislav Petkov
2021-04-07 21:43 ` Luck, Tony
2021-04-08 8:49 ` Borislav Petkov
2021-04-08 17:08 ` Luck, Tony
2021-04-13 10:07 ` Borislav Petkov
2021-04-13 16:13 ` Luck, Tony
2021-04-14 13:05 ` Borislav Petkov
2021-03-26 0:02 ` [PATCH 4/4] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-04-08 13:36 ` Borislav Petkov
2021-04-08 16:06 ` Luck, Tony
2021-04-08 2:13 ` [RFC 0/4] Fix machine check recovery for copy_from_user Aili Yao
2021-04-08 14:39 ` Luck, Tony
2021-04-09 6:49 ` Aili Yao
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