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| author | Andy Lutomirski <luto@amacapital.net> | 2014-12-17 14:48:30 -0800 |
|---|---|---|
| committer | Stefan Bader <stefan.bader@canonical.com> | 2015-05-29 11:54:13 +0200 |
| commit | 223b4f20aff3d305dd9789863e671b63aa8e10be (patch) | |
| tree | 3d22d33d2f4e6de71bb2cbef836f0b82219e35bc | |
| parent | e01303762385edef1cdd412f2703f1537b569aa7 (diff) | |
| download | linux-2.6.32.y-drm33.z-223b4f20aff3d305dd9789863e671b63aa8e10be.tar.gz | |
x86/tls: Don't validate lm in set_thread_area() after all
commit 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 upstream.
It turns out that there's a lurking ABI issue. GCC, when
compiling this in a 32-bit program:
struct user_desc desc = {
.entry_number = idx,
.base_addr = base,
.limit = 0xfffff,
.seg_32bit = 1,
.contents = 0, /* Data, grow-up */
.read_exec_only = 0,
.limit_in_pages = 1,
.seg_not_present = 0,
.useable = 0,
};
will leave .lm uninitialized. This means that anything in the
kernel that reads user_desc.lm for 32-bit tasks is unreliable.
Revert the .lm check in set_thread_area(). The value never did
anything in the first place.
Fixes: 0e58af4e1d21 ("x86/tls: Disallow unusual TLS segments")
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/d7875b60e28c512f6a6fc0baf5714d58e7eaadbb.1418856405.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit c759a579c902167d656ee303d518cb5eed2af278)
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
| -rw-r--r-- | arch/x86/include/asm/ldt.h | 7 | ||||
| -rw-r--r-- | arch/x86/kernel/tls.c | 6 |
2 files changed, 7 insertions, 6 deletions
diff --git a/arch/x86/include/asm/ldt.h b/arch/x86/include/asm/ldt.h index 46727eb37bfe20..6e1aaf73852ac9 100644 --- a/arch/x86/include/asm/ldt.h +++ b/arch/x86/include/asm/ldt.h @@ -28,6 +28,13 @@ struct user_desc { unsigned int seg_not_present:1; unsigned int useable:1; #ifdef __x86_64__ + /* + * Because this bit is not present in 32-bit user code, user + * programs can pass uninitialized values here. Therefore, in + * any context in which a user_desc comes from a 32-bit program, + * the kernel must act as though lm == 0, regardless of the + * actual value. + */ unsigned int lm:1; #endif }; diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c index 6146cc0ff5d437..0c38d06b379aec 100644 --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -77,12 +77,6 @@ static bool tls_desc_okay(const struct user_desc *info) if (info->seg_not_present) return false; -#ifdef CONFIG_X86_64 - /* The L bit makes no sense for data. */ - if (info->lm) - return false; -#endif - return true; } |