linux-kernel - [PATCH 4/8] signal/mips: Document a conflict with SI

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Message-Id: <20170630123906.8865-4-ebiederm@xmission.com>
Date:   Fri, 30 Jun 2017 07:39:02 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrei Vagin <avagin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>, Greg KH <greg@...ah.com>,
        Andrey Vagin <avagin@...nvz.org>,
        Serge Hallyn <serge@...lyn.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Willy Tarreau <w@....eu>, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thiemo Seufer <ths@...ux-mips.org>,
        Ralf Baechle <ralf@...ux-mips.org>
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@...ux-mips.org>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Ref: 948a34cf3988 ("[MIPS] Maintain si_code field properly for FP exceptions")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.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