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Subject[PATCH 4/8] signal/mips: Document a conflict with SI_USER with SIGFPE
Setting si_code to __SI_FAULT results in a userspace seeing
an si_code of 0. This is the same si_code as SI_USER. Posix
and common sense requires that SI_USER not be a signal specific
si_code. As such this use of 0 for the si_code is a pretty
horribly broken ABI.

This use of of __SI_FAULT is only a decade old. Which compared
to the other pieces of kernel code that has made this mistake
is almost yesterday.

This is probably worth fixing but I don't know mips well enough
to know what si_code to would be the proper one to use.

Cc: Thiemo Seufer <ths@linux-mips.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Ref: 948a34cf3988 ("[MIPS] Maintain si_code field properly for FP exceptions")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
arch/mips/include/uapi/asm/siginfo.h | 5 +++++
arch/mips/kernel/traps.c | 2 +-
2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/uapi/asm/siginfo.h b/arch/mips/include/uapi/asm/siginfo.h
index 8069cf766603..0d80df888325 100644
--- a/arch/mips/include/uapi/asm/siginfo.h
+++ b/arch/mips/include/uapi/asm/siginfo.h
@@ -123,4 +123,9 @@ typedef struct siginfo {
#define SI_TIMER __SI_CODE(__SI_TIMER, -3) /* sent by timer expiration */
#define SI_MESGQ __SI_CODE(__SI_MESGQ, -4) /* sent by real time mesq state change */

+/*
+ * SIGFPE si_codes
+ */
+#define FPE_FIXME (__SI_FAULT|0) /* Broken dup of SI_USER */
+
#endif /* _UAPI_ASM_SIGINFO_H */
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 9681b5877140..477dfca99147 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -732,7 +732,7 @@ void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
else if (fcr31 & FPU_CSR_INE_X)
si.si_code = FPE_FLTRES;
else
- si.si_code = __SI_FAULT;
+ si.si_code = FPE_FIXME;
force_sig_info(SIGFPE, &si, tsk);
}

--
2.10.1
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