linux-kernel - [PATCH 2.6.32 37/42] MIPS: Fix restart of indirect syscalls

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-Id: <20160123141223.589159555@1wt.eu>
Date:	Sat, 23 Jan 2016 15:12:58 +0100
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Ed Swierk <eswierk@...portsystems.com>, linux-mips@...ux-mips.org,
	Ralf Baechle <ralf@...ux-mips.org>,
	Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>
Subject: [PATCH 2.6.32 37/42] MIPS: Fix restart of indirect syscalls

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Ed Swierk <eswierk@...portsystems.com>

commit e967ef022e00bb7c2e5b1a42007abfdd52055050 upstream.

When 32-bit MIPS userspace invokes a syscall indirectly via syscall(number,
arg1, ..., arg7), the kernel looks up the actual syscall based on the given
number, shifts the other arguments to the left, and jumps to the syscall.

If the syscall is interrupted by a signal and indicates it needs to be
restarted by the kernel (by returning ERESTARTNOINTR for example), the
syscall must be called directly, since the number is no longer the first
argument, and the other arguments are now staged for a direct call.

Before shifting the arguments, store the syscall number in pt_regs->regs[2].
This gets copied temporarily into pt_regs->regs[0] after the syscall returns.
If the syscall needs to be restarted, handle_signal()/do_signal() copies the
number back to pt_regs->reg[2], which ends up in $v0 once control returns to
userspace.

Signed-off-by: Ed Swierk <eswierk@...portsystems.com>
Cc: linux-mips@...ux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8929/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
(cherry picked from commit 08f865bba9c705aef95268a33393698e5385587e)
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/mips/kernel/scall32-o32.S | 1 +
 arch/mips/kernel/scall64-o32.S | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
index b72c554..44194c1 100644
--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -194,6 +194,7 @@ illegal_syscall:
 	sll	t1, t0, 3
 	beqz	v0, einval
 	lw	t2, sys_call_table(t1)		# syscall routine
+	sw	a0, PT_R2(sp)			# call routine directly on restart

 	/* Some syscalls like execve get their arguments from struct pt_regs
 	   and claim zero arguments in the syscall table. Thus we have to
diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
index 33ed571..1f7c01f 100644
--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -180,6 +180,7 @@ LEAF(sys32_syscall)
 	dsll	t1, t0, 3
 	beqz	v0, einval
 	ld	t2, sys_call_table(t1)		# syscall routine
+	sd	a0, PT_R2(sp)		# call routine directly on restart

 	move	a0, a1			# shift argument registers
 	move	a1, a2
-- 
1.7.12.2.21.g234cd45.dirty