On Thu, Nov 11, 2021 at 11:11:00AM +0100, Marco Elver wrote:

On Tue, 5 Oct 2021 at 17:13, Marco Elver [off-list ref] wrote:

quoted

So this is where I'd like to hear if the approach of:

 | #if !defined(CONFIG_ARCH_WANTS_NO_INSTR) || defined(CONFIG_STACK_VALIDATION)
 | ...
 | #else
 | #define kcsan_noinstr noinstr
 | static __always_inline bool within_noinstr(unsigned long ip)
 | {
 |      return (unsigned long)__noinstr_text_start <= ip &&
 |             ip < (unsigned long)__noinstr_text_end;

Provided these turn into compile time constants this stands a fair
chance of working I suppose. Once this needs data loads things get a
*lot* more tricky.

quoted

 | }
 | #endif

and then (using the !STACK_VALIDATION definitions)

 | kcsan_noinstr void instrumentation_may_appear_in_noinstr(void)
 | {
 |      if (within_noinstr(_RET_IP_))
 |              return;

works for the non-x86 arches that select ARCH_WANTS_NO_INSTR.

If it doesn't I can easily just remove kcsan_noinstr/within_noinstr, and
add a "depends on !ARCH_WANTS_NO_INSTR || STACK_VALIDATION" to the
KCSAN_WEAK_MEMORY option.

Looking at a previous discussion [1], however, I was under the
impression that this would work.

[1] https://lkml.kernel.org/r/CANpmjNMAZiW-Er=2QDgGP+_3hg1LOvPYcbfGSPMv=aR6MVTB-g@mail.gmail.com

I'll send v2 of this series after 5.16-rc1. So far I think we haven't
been able to say the above doesn't work, which means I'll assume it
works on non-x86 architectures with ARCH_WANTS_NO_INSTR until we get
evidence of the opposite.

Fair enough.