From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bl2nam02on0111.outbound.protection.outlook.com ([104.47.38.111]:9280 "EHLO NAM02-BL2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S934079AbeCSPuS (ORCPT ); Mon, 19 Mar 2018 11:50:18 -0400 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: "Eric W. Biederman" , "James E.J. Bottomley" , Helge Deller , "linux-parisc@vger.kernel.org" , Sasha Levin Subject: [PATCH AUTOSEL for 4.15 118/124] signal/parisc: Document a conflict with SI_USER with SIGFPE Date: Mon, 19 Mar 2018 15:49:14 +0000 Message-ID: <20180319154645.11350-118-alexander.levin@microsoft.com> References: <20180319154645.11350-1-alexander.levin@microsoft.com> In-Reply-To: <20180319154645.11350-1-alexander.levin@microsoft.com> Content-Language: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org List-ID: From: "Eric W. Biederman" [ Upstream commit b5daf2b9d1c9a2b4f03ca93f75913ba2da3b3eaa ] Setting si_code to 0 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. Further use of si_code =3D=3D 0 guaranteed that copy_siginfo_to_user saw a value of __SI_KILL and now sees a value of SIL_KILL with the result that uid and pid fields are copied and which might copying the si_addr field by accident but certainly not by design. Making this a very flakey implementation. Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the appropriate fields will reliably be copied. This bug is 13 years old and parsic machines are no longer being built so I don't know if it possible or worth fixing it. But it is at least worth documenting this so other architectures don't make the same mistake. Possible ABI fixes includee: - Send the signal without siginfo - Don't generate a signal - Possibly assign and use an appropriate si_code - Don't handle cases which can't happen Cc: "James E.J. Bottomley" Cc: Helge Deller Cc: linux-parisc@vger.kernel.org Ref: 313c01d3e3fd ("[PATCH] PA-RISC update for 2.6.0") Histroy Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.= git Signed-off-by: "Eric W. Biederman" Signed-off-by: Sasha Levin --- arch/parisc/include/uapi/asm/siginfo.h | 7 +++++++ arch/parisc/kernel/traps.c | 2 +- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/parisc/include/uapi/asm/siginfo.h b/arch/parisc/include/u= api/asm/siginfo.h index 4a1062e05aaf..be40331f757d 100644 --- a/arch/parisc/include/uapi/asm/siginfo.h +++ b/arch/parisc/include/uapi/asm/siginfo.h @@ -8,4 +8,11 @@ =20 #include =20 +/* + * SIGFPE si_codes + */ +#ifdef __KERNEL__ +#define FPE_FIXME 0 /* Broken dup of SI_USER */ +#endif /* __KERNEL__ */ + #endif diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c index 8453724b8009..c919e6c0a687 100644 --- a/arch/parisc/kernel/traps.c +++ b/arch/parisc/kernel/traps.c @@ -629,7 +629,7 @@ void notrace handle_interruption(int code, struct pt_re= gs *regs) si.si_signo =3D SIGFPE; /* Set to zero, and let the userspace app figure it out from the insn pointed to by si_addr */ - si.si_code =3D 0; + si.si_code =3D FPE_FIXME; si.si_addr =3D (void __user *) regs->iaoq[0]; force_sig_info(SIGFPE, &si, current); return; --=20 2.14.1