diff options
| author | H. Peter Anvin <hpa@linux.intel.com> | 2014-03-16 15:31:54 -0700 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2014-12-13 15:16:07 +0100 |
| commit | 1d97cac8c0469759c979e9f2d48ef4122c543e3d (patch) | |
| tree | cca4e9a48eba7228c11500fe3efbb620245a45e8 /arch | |
| parent | ddd12e4e3fdbd0906fe30aef5b51ecebc71d2af6 (diff) | |
x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels
commit b3b42ac2cbae1f3cecbb6229964a4d48af31d382 upstream.
The IRET instruction, when returning to a 16-bit segment, only
restores the bottom 16 bits of the user space stack pointer. We have
a software workaround for that ("espfix") for the 32-bit kernel, but
it relies on a nonzero stack segment base which is not available in
32-bit mode.
Since 16-bit support is somewhat crippled anyway on a 64-bit kernel
(no V86 mode), and most (if not quite all) 64-bit processors support
virtualization for the users who really need it, simply reject
attempts at creating a 16-bit segment when running on top of a 64-bit
kernel.
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/n/tip-kicdm89kzw9lldryb1br9od0@git.kernel.org
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from 3.2 commit a862b5c4076b1ba4dd6c87aebac478853dc6db47)
Signed-off-by: Willy Tarreau <w@1wt.eu>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/ldt.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index ec6ef60cbd17..75e356c5870c 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -229,6 +229,17 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) } } + /* + * On x86-64 we do not support 16-bit segments due to + * IRET leaking the high bits of the kernel stack address. + */ +#ifdef CONFIG_X86_64 + if (!ldt_info.seg_32bit) { + error = -EINVAL; + goto out_unlock; + } +#endif + fill_ldt(&ldt, &ldt_info); if (oldmode) ldt.avl = 0; |