diff options
| author | Andy Lutomirski <luto@amacapital.net> | 2014-12-18 01:48:30 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2014-12-18 14:12:26 +0300 |
| commit | 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 (patch) | |
| tree | 497a40782e96617b59efa507aa736bd09c037452 | |
| parent | 0e58af4e1d2166e9e33375a0f121e4867010d4f8 (diff) | |
| download | linux-3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0.tar.xz | |
x86/tls: Don't validate lm in set_thread_area() after all
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: stable@vger.kernel.org # Only if 0e58af4e1d21 is backported
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>
| -rw-r--r-- | arch/x86/include/uapi/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/uapi/asm/ldt.h b/arch/x86/include/uapi/asm/ldt.h index 46727eb37bfe..6e1aaf73852a 100644 --- a/arch/x86/include/uapi/asm/ldt.h +++ b/arch/x86/include/uapi/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 3e551eee87b9..4e942f31b1a7 100644 --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -55,12 +55,6 @@ 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; } |