From: Mark Rutland <mark.rutland@arm.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, linux-kernel@vger.kernel.org, elver@google.com,
jbaron@akamai.com, rostedt@goodmis.org, ardb@kernel.org,
kernel test robot <lkp@intel.com>
Subject: Re: [PATCH 2/3] x86/cpu: Elide KCSAN for cpu_has() and friends
Date: Tue, 3 May 2022 15:20:06 +0100 [thread overview]
Message-ID: <YnE6Fjums+jTH96Y@lakrids> (raw)
In-Reply-To: <20220502184747.cr5ssem3g4mel4qq@treble>
On Mon, May 02, 2022 at 11:47:47AM -0700, Josh Poimboeuf wrote:
> On Mon, May 02, 2022 at 01:07:43PM +0200, Peter Zijlstra wrote:
> > vmlinux.o: warning: objtool: enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x28: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0x24: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
> >
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> An explanation about *why* this fixes it would help, as I have no idea
> from looking at the patch.
How about something like:
| As x86 uses the <asm-generic/bitops/instrumented-*.h> headers, the
| regular forms of all bitops are instrumented with explicit calls to
| KASAN and KCSAN checks. As these are explicit calls, these are not
| suppressed by the noinstr function attribute.
|
| This can result in calls to those check functions in noinstr code, which
| objtool warns about:
|
| vmlinux.o: warning: objtool: enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
| vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x28: call to __kcsan_check_access() leaves .noinstr.text section
| vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0x24: call to __kcsan_check_access() leaves .noinstr.text section
| vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
|
| Prevent this by using the arch_*() bitops, which are the underlying
| bitops without explciit instrumentation.
Thanks,
Mark.
>
> > ---
> > arch/x86/include/asm/cpufeature.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > --- a/arch/x86/include/asm/cpufeature.h
> > +++ b/arch/x86/include/asm/cpufeature.h
> > @@ -51,7 +51,7 @@ extern const char * const x86_power_flag
> > extern const char * const x86_bug_flags[NBUGINTS*32];
> >
> > #define test_cpu_cap(c, bit) \
> > - test_bit(bit, (unsigned long *)((c)->x86_capability))
> > + arch_test_bit(bit, (unsigned long *)((c)->x86_capability))
> >
> > /*
> > * There are 32 bits/features in each mask word. The high bits
> >
> >
>
> --
> Josh
>
next prev parent reply other threads:[~2022-05-03 14:20 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-02 11:07 [PATCH 0/3] x86: Address various objtool complaints Peter Zijlstra
2022-05-02 11:07 ` [PATCH 1/3] objtool: Mark __ubsan_handle_builtin_unreachable() as noreturn Peter Zijlstra
2022-05-02 11:07 ` [PATCH 2/3] x86/cpu: Elide KCSAN for cpu_has() and friends Peter Zijlstra
2022-05-02 11:54 ` Marco Elver
2022-05-02 18:47 ` Josh Poimboeuf
2022-05-03 14:20 ` Mark Rutland [this message]
2022-05-30 10:38 ` [tip: objtool/urgent] " tip-bot2 for Peter Zijlstra
2022-05-02 11:07 ` [PATCH 3/3] jump_label,noinstr: Avoid instrumentation for JUMP_LABEL=n builds Peter Zijlstra
2022-05-02 11:23 ` Marco Elver
2022-05-02 13:01 ` Peter Zijlstra
2022-05-02 13:09 ` [PATCH v2 " Peter Zijlstra
2022-05-02 13:25 ` Marco Elver
2022-05-02 14:54 ` Peter Zijlstra
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