From: Tong Tiangen <tongtiangen@huawei.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Robin Murphy <robin.murphy@arm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, <x86@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
<linuxppc-dev@lists.ozlabs.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
Xie XiuQi <xiexiuqi@huawei.com>, Guohanjun <guohanjun@huawei.com>
Subject: Re: [PATCH -next v5 7/8] arm64: add uaccess to machine check safe
Date: Mon, 20 Jun 2022 10:04:42 +0800 [thread overview]
Message-ID: <7d50dcb8-8a7c-5735-cd49-ad814fecf641@huawei.com> (raw)
In-Reply-To: <Yq24TSpZK+3/86Pj@FVFF77S0Q05N>
在 2022/6/18 19:35, Mark Rutland 写道:
> On Sat, Jun 18, 2022 at 05:27:45PM +0800, Tong Tiangen wrote:
>>
>>
>> 在 2022/6/17 17:06, Mark Rutland 写道:
>>> 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 <tongtiangen@huawei.com>
>>>
>>>> ---
>>>> 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.
>>
>> You have a point. so there is no need to modify copy_from/to_user.S in this
>> patch set.
>
> Cool, thanks. If this patch just has the extable change, that's fine by me.
>
>>> 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 recovery success, The task will be killed and there will be no subsequent
>> memset().
>
> I don't think that's true.
>
> IIUC per the last patch, in the exception handler we'll apply the fixup then
> force a signal. That doesn't kill the task immediately, and we'll return from
> the exception handler back into the original context (with the fixup applied).
>
correct.
> The structure of copy_from_user() is
>
> copy_from_user(to, from, n) {
> _copy_from_user(to, from, n) {
> res = n;
> res = raw_copy_from_user(to, from, n);
> if (res)
> memset(to + (n - res), 0, res);
> }
> }
>
> So when the fixup is applied and res indicates that the copy terminated early,
> there is an unconditinal memset() before the fatal signal is handled in the
> return to userspace path.
correct in this scenario.
My idea is also valuable in many other scenarios.
>
>>> 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.
>
> [...]
>
>>>> diff --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?
>>
>> According to my understanding of the above, only the modification of
>> extable.c is retained.
>>
>> So what do you mean which part is made into a separate patch?
>
> As above, if you just retain the extable.c changes, that's fine by me.
Thanks,
Tong.
>
> Thanks,
> Mark.
> .
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-06-20 2:06 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-28 6:50 [PATCH -next v5 0/8]arm64: add machine check safe support Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 1/8] arm64: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support Tong Tiangen
2022-06-17 8:23 ` Mark Rutland
2022-06-18 2:44 ` Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use extable type EX_TYPE_UACCESS_ERR_ZERO Tong Tiangen
2022-06-17 8:24 ` Mark Rutland
2022-06-18 3:26 ` Tong Tiangen
2022-06-18 8:42 ` Tong Tiangen
2022-06-18 12:40 ` Mark Rutland
2022-06-20 2:59 ` Tong Tiangen
2022-06-20 9:10 ` Mark Rutland
2022-06-20 13:32 ` Tong Tiangen
2022-06-20 14:13 ` Tong Tiangen
2022-06-20 14:26 ` Mark Rutland
2022-05-28 6:50 ` [PATCH -next v5 3/8] arm64: extable: move _cond_extable to _cond_uaccess_extable Tong Tiangen
2022-06-17 8:31 ` Mark Rutland
2022-05-28 6:50 ` [PATCH -next v5 4/8] arm64: extable: cleanup redundant extable type EX_TYPE_FIXUP Tong Tiangen
2022-06-17 8:43 ` Mark Rutland
2022-05-28 6:50 ` [PATCH -next v5 5/8] Add generic fallback version of copy_mc_to_user() Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 6/8] arm64: add support for machine check error safe Tong Tiangen
2022-06-17 8:55 ` Mark Rutland
2022-06-18 9:18 ` Tong Tiangen
2022-06-18 12:52 ` Mark Rutland
2022-06-20 1:53 ` Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 7/8] arm64: add uaccess to machine check safe Tong Tiangen
2022-06-17 9:06 ` Mark Rutland
2022-06-18 9:27 ` Tong Tiangen
2022-06-18 11:35 ` Mark Rutland
2022-06-20 2:04 ` Tong Tiangen [this message]
2022-05-28 6:50 ` [PATCH -next v5 8/8] arm64: add cow " Tong Tiangen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=7d50dcb8-8a7c-5735-cd49-ad814fecf641@huawei.com \
--to=tongtiangen@huawei.com \
--cc=akpm@linux-foundation.org \
--cc=benh@kernel.crashing.org \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=dave.hansen@linux.intel.com \
--cc=guohanjun@huawei.com \
--cc=hpa@zytor.com \
--cc=james.morse@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=mpe@ellerman.id.au \
--cc=paulus@samba.org \
--cc=robin.murphy@arm.com \
--cc=tglx@linutronix.de \
--cc=viro@zeniv.linux.org.uk \
--cc=wangkefeng.wang@huawei.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
--cc=xiexiuqi@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).