Re: [PATCH 2/2] sigaction.2: wfix - Clarify si_addr description.

On 3/8/2021 1:30 PM, Borislav Petkov wrote:

On Fri, Feb 26, 2021 at 09:26:34AM -0800, Yu-cheng Yu wrote:

quoted

SIGSEGV fills si_addr only for memory access faults.  Add a note to clarify.

Signed-off-by: Yu-cheng Yu <redacted>
Cc: Alejandro Colomar <redacted>
Cc: Michael Kerrisk <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Florian Weimer <redacted>
Cc: "H.J. Lu" <redacted>
Cc: linux-kernel@vger.kernel.org
Cc: linux-api@vger.kenel.org
Link: https://lore.kernel.org/linux-api/20210217222730.15819-7-yu-cheng.yu@intel.com/
---
  man2/sigaction.2 | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/man2/sigaction.2 b/man2/sigaction.2
index 49a30f11e..bea884a23 100644
--- a/man2/sigaction.2
+++ b/man2/sigaction.2

@@ -467,7 +467,7 @@ and
  .BR SIGTRAP
  fill in
  .I si_addr
-with the address of the fault.
+with the address of the fault (see notes).
  On some architectures,
  these signals also fill in the
  .I si_trapno

@@ -955,6 +955,11 @@ It is not possible to block
  .IR sa_mask ).
  Attempts to do so are silently ignored.
  .PP
+In a
+.B SIGSEGV,
+if the fault is a memory access fault, si_addr is filled with the address
+causing the fault, otherwise it is not filled.

"... otherwise it is uninitialized." or "zeroed" or whatever...

And I'm having trouble figuring out why do you need to clarify this?

Because of this sentence:

        * SIGILL,  SIGFPE, SIGSEGV, SIGBUS, and SIGTRAP fill in si_addr with the address
          of the fault.  On some architectures, these signals also fill in the si_trapno
          field.

?

I think the sentence above is vague, but probably for the reason that 
each arch is different.  Maybe this patch is unnecessary and can be dropped?

If so, did you audit all architectures whether si_addr is populated only
on memory access faults or is this something POSIX dictates or what's
up? Because the sigaction(2) manpage is arch-agnostic and this is a
rather strong assertion.

What am I missing?

Thx.

On Mon, Mar 08, 2021 at 01:46:07PM -0800, Yu, Yu-cheng wrote:

I think the sentence above is vague, but probably for the reason that each
arch is different.  Maybe this patch is unnecessary and can be dropped?

Maybe.

If you want to clarify it, you should audit every arch. But what
would that bring? IOW, is it that important to specify when si_addr
is populated and when not...? I don't know of an example but I'm
no userspace programmer anyway, to know when this info would be
beneficial...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette