Messages in this thread | | | Date | Tue, 3 May 2022 15:20:06 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 2/3] x86/cpu: Elide KCSAN for cpu_has() and friends |
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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 >
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