From: Tong Tiangen <tongtiangen@huawei.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, <wangkefeng.wang@huawei.com>,
Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>, Tony Luck <tony.luck@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
<linux-kernel@vger.kernel.org>, <linux-edac@vger.kernel.org>,
<linux-mm@kvack.org>, Guohanjun <guohanjun@huawei.com>
Subject: Re: [PATCH -next v5 2/3] x86/mce: set MCE_IN_KERNEL_COPYIN for DEFAULT_MCE_SAFE exception
Date: Thu, 8 Feb 2024 14:21:05 +0800 [thread overview]
Message-ID: <34957b85-717a-055b-6b9b-5af16e57c31f@huawei.com> (raw)
In-Reply-To: <20240207122942.GRZcN3tqWkV-WE-pak@fat_crate.local>
在 2024/2/7 20:29, Borislav Petkov 写道:
> On Sun, Feb 04, 2024 at 04:26:26PM +0800, Tong Tiangen wrote:
>> diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
>> index bca780fa5e57..b2cce1b6c96d 100644
>> --- a/arch/x86/kernel/cpu/mce/severity.c
>> +++ b/arch/x86/kernel/cpu/mce/severity.c
>> @@ -292,11 +292,11 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
>> case EX_TYPE_UACCESS:
>> if (!copy_user)
>> return IN_KERNEL;
>> + fallthrough;
>> + case EX_TYPE_DEFAULT_MCE_SAFE:
>> m->kflags |= MCE_IN_KERNEL_COPYIN;
>> fallthrough;
>
> I knew something was still bugging me here and this is still wrong.
>
> Let's imagine this flow:
>
> copy_mc_to_user() - note *src is kernel memory
> |-> copy_mc_enhanced_fast_string or copy_mc_fragile - it's the same thing
> |-> -#MC, exception type EX_TYPE_DEFAULT_MCE_SAFE
> |-> error_context():
> case EX_TYPE_DEFAULT_MCE_SAFE:
> m->kflags |= MCE_IN_KERNEL_COPYIN;
>
> MCE_IN_KERNEL_COPYIN does kill_me_never():
>
> pr_err("Kernel accessed poison in user space at %llx\n", p->mce_addr);
>
> but that's reading from kernel memory!
>
> IOW, I *think* that switch statement should be this:
>
> switch (fixup_type) {
> case EX_TYPE_UACCESS:
> case EX_TYPE_DEFAULT_MCE_SAFE:
> if (!copy_user)
> return IN_KERNEL;
>
> m->kflags |= MCE_IN_KERNEL_COPYIN;
> fallthrough;
>
> case EX_TYPE_FAULT_MCE_SAFE:
> m->kflags |= MCE_IN_KERNEL_RECOV;
> return IN_KERNEL_RECOV;
>
> default:
> return IN_KERNEL;
> }
>
> Provided I'm not missing a case and provided is_copy_from_user() really
> detects all cases properly.
>
> And then patch 3 is wrong because we only can handle "copy in" - not
> just any copy.
That makes sense. I'll check that point out later.
Many thanks.
Tong.
>
> Thx.
>
next prev parent reply other threads:[~2024-02-08 6:21 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-04 8:26 [PATCH -next v5 0/3] minor improvements for x86 mce processing Tong Tiangen
2024-02-04 8:26 ` [PATCH -next v5 1/3] x86/mce: remove redundant fixup type EX_TYPE_COPY Tong Tiangen
2024-02-04 8:26 ` [PATCH -next v5 2/3] x86/mce: set MCE_IN_KERNEL_COPYIN for DEFAULT_MCE_SAFE exception Tong Tiangen
2024-02-07 12:29 ` Borislav Petkov
2024-02-08 6:21 ` Tong Tiangen [this message]
2024-02-18 10:08 ` Tong Tiangen
2024-03-27 0:48 ` Tong Tiangen
2024-03-27 22:05 ` Borislav Petkov
2024-04-01 3:41 ` Tong Tiangen
2024-02-04 8:26 ` [PATCH -next v5 3/3] x86/mce: rename MCE_IN_KERNEL_COPYIN to MCE_IN_KERNEL_COPY_MC Tong Tiangen
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