Re: sparc/ppc/arm compat siginfo ABI regressions: sending SIGFPE via kill() returns wrong values in si_pid and si_uid

[Linus Torvalds]

On Fri, Apr 13, 2018 at 2:42 AM, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxx> wrote:
>
> Yes, it does solve the problem at hand with strace - the exact patch I
> tested against 4.16 is below.

Ok, good.

> However, FPE_FLTUNK is not defined in older kernels, so while we can
> fix it this way for the current merge window, that doesn't help 4.16.

I wonder if we should even bother with FPE_FLTUNK.

I suspect we might as well use FPE_FLTINV, I suspect, and not have
this complexity at all. That case is not worth worrying about, since
it's a "this shouldn't happen anyway" and the *real* reason will be in
the kernel logs due to vfs_panic().

So it's not like this is something that the user should ever care
about the si_code about.

> Given that the path we're talking about is unlikely to happen (as
> mentioned in my second paragraph) I still think reverting Eric's patch
> is the right way forward for older kernels.

I'd much rather get rid of that FPE_FIXME, and leave that whole mess behind.

So the attached patch seems simple and should work with 4.16 too.

Let's not leave this as some kind of nasty maintenance issue, and just
go for simple and stupid.

Hmm?

                Linus
 arch/arm/include/uapi/asm/siginfo.h | 13 -------------
 arch/arm/vfp/vfpmodule.c            |  2 +-
 2 files changed, 1 insertion(+), 14 deletions(-)

diff --git a/arch/arm/include/uapi/asm/siginfo.h b/arch/arm/include/uapi/asm/siginfo.h
deleted file mode 100644
index d0513880be21..000000000000
--- a/arch/arm/include/uapi/asm/siginfo.h
+++ /dev/null
@@ -1,13 +0,0 @@
-#ifndef __ASM_SIGINFO_H
-#define __ASM_SIGINFO_H
-
-#include <asm-generic/siginfo.h>
-
-/*
- * SIGFPE si_codes
- */
-#ifdef __KERNEL__
-#define FPE_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-#endif
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 4c375e11ae95..af4ee2cef2f9 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -257,7 +257,7 @@ static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_
 
 	if (exceptions == VFP_EXCEPTION_ERROR) {
 		vfp_panic("unhandled bounce", inst);
-		vfp_raise_sigfpe(FPE_FIXME, regs);
+		vfp_raise_sigfpe(FPE_FLTINV, regs);
 		return;
 	}