From 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 17 Dec 2014 14:48:30 -0800 Subject: 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 Acked-by: Thomas Gleixner Cc: stable@vger.kernel.org # Only if 0e58af4e1d21 is backported Cc: Linus Torvalds Link: http://lkml.kernel.org/r/d7875b60e28c512f6a6fc0baf5714d58e7eaadbb.1418856405.git.luto@amacapital.net Signed-off-by: Ingo Molnar --- arch/x86/kernel/tls.c | 6 ------ 1 file changed, 6 deletions(-) (limited to 'arch/x86/kernel') 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; } -- cgit v1.2.3-59-g8ed1b