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authorAndy Lutomirski <luto@amacapital.net>2014-12-17 14:48:30 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-01-08 09:58:15 -0800
commitd011d586b3f9f1b08f3deb080d8542f56963dc28 (patch)
tree822c4c9f9496620844d252b97e1e2eb808748a8d
parent81f250e1cf8048e4780e46d5219b0e7f943a336b (diff)
downloadlinux-linaro-stable-d011d586b3f9f1b08f3deb080d8542f56963dc28.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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/x86/include/uapi/asm/ldt.h7
-rw-r--r--arch/x86/kernel/tls.c6
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;
}