x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue
authorAndy Lutomirski <luto@kernel.org>
Sun, 26 Apr 2015 23:47:59 +0000 (16:47 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Mon, 27 Apr 2015 00:57:38 +0000 (17:57 -0700)
commit61f01dd941ba9e06d2bf05994450ecc3d61b6b8b
tree3a4a4ef2d5e4d44bb4cb1708f9fc4749e9c9824a
parent1190944f4b12203330ac5ed8784f6c181bf26f2d
x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

AMD CPUs don't reinitialize the SS descriptor on SYSRET, so SYSRET with
SS == 0 results in an invalid usermode state in which SS is apparently
equal to __USER_DS but causes #SS if used.

Work around the issue by setting SS to __KERNEL_DS __switch_to, thus
ensuring that SYSRET never happens with SS set to NULL.

This was exposed by a recent vDSO cleanup.

Fixes: e7d6eefaaa44 x86/vdso32/syscall.S: Do not load __USER32_DS to %ss
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
arch/x86/ia32/ia32entry.S
arch/x86/include/asm/cpufeature.h
arch/x86/kernel/cpu/amd.c
arch/x86/kernel/entry_64.S
arch/x86/kernel/process_64.c