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Subject[PATCH 3.4 080/176] x86, um: actually mark system call tables readonly
Date
From: Daniel Borkmann <dborkman@redhat.com>

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

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


commit b485342bd79af363c77ef1a421c4a0aef2de9812 upstream.

Commit a074335a370e ("x86, um: Mark system call tables readonly") was
supposed to mark the sys_call_table in UML as RO by adding the const,
but it doesn't have the desired effect as it's nevertheless being placed
into the data section since __cacheline_aligned enforces sys_call_table
being placed into .data..cacheline_aligned instead. We need to use
the ____cacheline_aligned version instead to fix this issue.

Before:

$ nm -v arch/x86/um/sys_call_table_64.o | grep -1 "sys_call_table"
U sys_writev
0000000000000000 D sys_call_table
0000000000000000 D syscall_table_size

After:

$ nm -v arch/x86/um/sys_call_table_64.o | grep -1 "sys_call_table"
U sys_writev
0000000000000000 R sys_call_table
0000000000000000 D syscall_table_size

Fixes: a074335a370e ("x86, um: Mark system call tables readonly")
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
arch/x86/um/sys_call_table_32.c | 2 +-
arch/x86/um/sys_call_table_64.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/um/sys_call_table_32.c b/arch/x86/um/sys_call_table_32.c
index 68d1dc9..bd8b159 100644
--- a/arch/x86/um/sys_call_table_32.c
+++ b/arch/x86/um/sys_call_table_32.c
@@ -43,7 +43,7 @@ typedef asmlinkage void (*sys_call_ptr_t)(void);

extern asmlinkage void sys_ni_syscall(void);

-const sys_call_ptr_t sys_call_table[] __cacheline_aligned = {
+const sys_call_ptr_t sys_call_table[] ____cacheline_aligned = {
/*
* Smells like a compiler bug -- it doesn't work
* when the & below is removed.
diff --git a/arch/x86/um/sys_call_table_64.c b/arch/x86/um/sys_call_table_64.c
index 9924776..cbdab94 100644
--- a/arch/x86/um/sys_call_table_64.c
+++ b/arch/x86/um/sys_call_table_64.c
@@ -48,7 +48,7 @@ typedef void (*sys_call_ptr_t)(void);

extern void sys_ni_syscall(void);

-const sys_call_ptr_t sys_call_table[] __cacheline_aligned = {
+const sys_call_ptr_t sys_call_table[] ____cacheline_aligned = {
/*
* Smells like a compiler bug -- it doesn't work
* when the & below is removed.
--
1.9.1


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