From: Borislav Petkov <bp@alien8.de>
To: Tong Tiangen <tongtiangen@huawei.com>
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: Wed, 7 Feb 2024 13:29:42 +0100 [thread overview]
Message-ID: <20240207122942.GRZcN3tqWkV-WE-pak@fat_crate.local> (raw)
In-Reply-To: <20240204082627.3892816-3-tongtiangen@huawei.com>
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.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2024-02-07 12:30 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 [this message]
2024-02-08 6:21 ` Tong Tiangen
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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