From 61f01dd941ba9e06d2bf05994450ecc3d61b6b8b Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sun, 26 Apr 2015 16:47:59 -0700 Subject: 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 Cc: Peter Anvin Cc: Borislav Petkov Cc: Denys Vlasenko Cc: Brian Gerst Signed-off-by: Linus Torvalds --- arch/x86/kernel/cpu/amd.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/x86/kernel/cpu/amd.c') diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index fd470ebf924e..e4cf63301ff4 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -720,6 +720,9 @@ static void init_amd(struct cpuinfo_x86 *c) if (!cpu_has(c, X86_FEATURE_3DNOWPREFETCH)) if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM)) set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH); + + /* AMD CPUs don't reset SS attributes on SYSRET */ + set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); } #ifdef CONFIG_X86_32 -- cgit v1.2.3-55-g7522