linux-kernel - [PATCH 3.16 058/192] MIPS: Save static registers before sysmips

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Message-ID: <lsq.1507553064.738780694@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:44:24 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Ralf Baechle" <ralf@...ux-mips.org>,
        linux-mips@...ux-mips.org, "James Hogan" <james.hogan@...tec.com>
Subject: [PATCH 3.16 058/192] MIPS: Save static registers before sysmips

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

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

From: James Hogan <james.hogan@...tec.com>

commit 49955d84cd9ccdca5a16a495e448e1a06fad9e49 upstream.

The MIPS sysmips system call handler may return directly from the
MIPS_ATOMIC_SET case (mips_atomic_set()) to syscall_exit. This path
restores the static (callee saved) registers, however they won't have
been saved on entry to the system call.

Use the save_static_function() macro to create a __sys_sysmips wrapper
function which saves the static registers before calling sys_sysmips, so
that the correct static register state is restored by syscall_exit.

Fixes: f1e39a4a616c ("MIPS: Rewrite sysmips(MIPS_ATOMIC_SET, ...) in C with inline assembler")
Signed-off-by: James Hogan <james.hogan@...tec.com>
Cc: linux-mips@...ux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16149/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/mips/kernel/scall32-o32.S | 2 +-
 arch/mips/kernel/scall64-64.S  | 2 +-
 arch/mips/kernel/scall64-n32.S | 2 +-
 arch/mips/kernel/scall64-o32.S | 2 +-
 arch/mips/kernel/syscall.c     | 6 ++++++
 5 files changed, 10 insertions(+), 4 deletions(-)

--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -363,7 +363,7 @@ EXPORT(sys_call_table)
 	PTR	sys_writev
 	PTR	sys_cacheflush
 	PTR	sys_cachectl
-	PTR	sys_sysmips
+	PTR	__sys_sysmips
 	PTR	sys_ni_syscall			/* 4150 */
 	PTR	sys_getsid
 	PTR	sys_fdatasync
--- a/arch/mips/kernel/scall64-64.S
+++ b/arch/mips/kernel/scall64-64.S
@@ -318,7 +318,7 @@ EXPORT(sys_call_table)
 	PTR	sys_sched_getaffinity
 	PTR	sys_cacheflush
 	PTR	sys_cachectl
-	PTR	sys_sysmips
+	PTR	__sys_sysmips
 	PTR	sys_io_setup			/* 5200 */
 	PTR	sys_io_destroy
 	PTR	sys_io_getevents
--- a/arch/mips/kernel/scall64-n32.S
+++ b/arch/mips/kernel/scall64-n32.S
@@ -307,7 +307,7 @@ EXPORT(sysn32_call_table)
 	PTR	compat_sys_sched_getaffinity
 	PTR	sys_cacheflush
 	PTR	sys_cachectl
-	PTR	sys_sysmips
+	PTR	__sys_sysmips
 	PTR	compat_sys_io_setup			/* 6200 */
 	PTR	sys_io_destroy
 	PTR	compat_sys_io_getevents
--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -358,7 +358,7 @@ EXPORT(sys32_call_table)
 	PTR	compat_sys_writev
 	PTR	sys_cacheflush
 	PTR	sys_cachectl
-	PTR	sys_sysmips
+	PTR	__sys_sysmips
 	PTR	sys_ni_syscall			/* 4150 */
 	PTR	sys_getsid
 	PTR	sys_fdatasync
--- a/arch/mips/kernel/syscall.c
+++ b/arch/mips/kernel/syscall.c
@@ -197,6 +197,12 @@ static inline int mips_atomic_set(unsign
 	unreachable();
 }
 
+/*
+ * mips_atomic_set() normally returns directly via syscall_exit potentially
+ * clobbering static registers, so be sure to preserve them.
+ */
+save_static_function(sys_sysmips);
+
 SYSCALL_DEFINE3(sysmips, long, cmd, long, arg1, long, arg2)
 {
 	switch (cmd) {