From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave.hansen@intel.com>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
LKML <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2] x86: disable non-instrumented version of copy_mc when KMSAN is enabled
Date: Tue, 05 Mar 2024 17:50:51 +0100 [thread overview]
Message-ID: <87jzmgvd04.ffs@tglx> (raw)
In-Reply-To: <74d900cf-ab90-49ea-ba55-380d7df59526@intel.com>
On Tue, Mar 05 2024 at 07:21, Dave Hansen wrote:
> On 3/1/24 14:52, Tetsuo Handa wrote:
>> - if (static_cpu_has(X86_FEATURE_ERMS)) {
>> + if (!IS_ENABLED(CONFIG_KMSAN) && static_cpu_has(X86_FEATURE_ERMS)) {
>> __uaccess_begin();
>> ret = copy_mc_enhanced_fast_string((__force void *)dst, src, len);
>> __uaccess_end();
>
> Where does the false positive _come_ from? Can we fix copy_mc_fragile()
> and copy_mc_enhanced_fast_string() instead of just not using them?
All it takes is a variant of __msan_memcpy() which uses a variant of
copy_mc_to_kernel() instead of __memcpy(). It's not rocket science.
Aside of that, this:
@@ -74,14 +74,14 @@ unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, un
{
unsigned long ret;
- if (copy_mc_fragile_enabled) {
+ if (!IS_ENABLED(CONFIG_KMSAN) && copy_mc_fragile_enabled) {
__uaccess_begin();
is completely bogus. copy_user_generic() is not at all covered by
KMSAN. So why fiddling with it in the first place? Just because it has
the same pattern as copy_mc_to_kernel()?
> The three enable_copy_mc_fragile() are presumably doing so for a
> reason.
Very much so. It's for MCE recovery purposes.
And yes, the changelog and the non-existing comments should explain why
this is "correct" when KMSAN is enabled. Hint: It is NOT.
Thanks,
tglx
prev parent reply other threads:[~2024-03-05 16:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-01 22:52 [PATCH v2] x86: disable non-instrumented version of copy_mc when KMSAN is enabled Tetsuo Handa
2024-03-05 11:31 ` Tetsuo Handa
2024-03-05 16:22 ` Thomas Gleixner
2024-03-05 17:57 ` Linus Torvalds
2024-03-06 22:08 ` Tetsuo Handa
2024-03-07 0:09 ` Linus Torvalds
2024-03-19 12:38 ` Alexander Potapenko
2024-03-06 9:16 ` Ingo Molnar
2024-03-06 10:12 ` Tetsuo Handa
2024-03-05 15:21 ` Dave Hansen
2024-03-05 16:50 ` Thomas Gleixner [this message]
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