From: Andy Lutomirski <luto@kernel.org>
Date: Sun, 26 Apr 2015 23:47:59 +0000 (-0700)
Subject: x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue
X-Git-Tag: omap-for-v4.2/o2_dc~4
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=61f01dd941ba;p=pandora-kernel.git

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>
---

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