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Message-ID: <74d900cf-ab90-49ea-ba55-380d7df59526@intel.com>
Date: Tue, 5 Mar 2024 07:21:38 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
LKML <linux-kernel@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2] x86: disable non-instrumented version of copy_mc when
KMSAN is enabled
On 3/1/24 14:52, Tetsuo Handa wrote:
> unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len)
> {
> - if (copy_mc_fragile_enabled)
> + if (!IS_ENABLED(CONFIG_KMSAN) && copy_mc_fragile_enabled)
> return copy_mc_fragile(dst, src, len);
> - if (static_cpu_has(X86_FEATURE_ERMS))
> + if (!IS_ENABLED(CONFIG_KMSAN) && static_cpu_has(X86_FEATURE_ERMS))
> return copy_mc_enhanced_fast_string(dst, src, len);
> memcpy(dst, src, len);
> return 0;
> @@ -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();
> ret = copy_mc_fragile((__force void *)dst, src, len);
> __uaccess_end();
> return ret;
> }
>
> - 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?
The three enable_copy_mc_fragile() are presumably doing so for a reason.
What is this patch's impact on _those_?
Third, instead of sprinkling IS_ENABLED(CONFIG_KMSAN) checks in random
spots, can we do this in a central spot?
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