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| author | Andy Lutomirski <luto@kernel.org> | 2015-04-26 16:47:59 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-04-26 17:57:38 -0700 |
| commit | 61f01dd941ba9e06d2bf05994450ecc3d61b6b8b (patch) | |
| tree | 3a4a4ef2d5e4d44bb4cb1708f9fc4749e9c9824a /arch/x86/ia32 | |
| parent | 1190944f4b12203330ac5ed8784f6c181bf26f2d (diff) | |
| download | linux-61f01dd941ba9e06d2bf05994450ecc3d61b6b8b.tar.bz2 | |
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>
Diffstat (limited to 'arch/x86/ia32')
| -rw-r--r-- | arch/x86/ia32/ia32entry.S | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index a821b1cd4fa7..72bf2680f819 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -427,6 +427,13 @@ sysretl_from_sys_call: * cs and ss are loaded from MSRs. * (Note: 32bit->32bit SYSRET is different: since r11 * does not exist, it merely sets eflags.IF=1). + * + * NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss + * descriptor is not reinitialized. This means that we must + * avoid SYSRET with SS == NULL, which could happen if we schedule, + * exit the kernel, and re-enter using an interrupt vector. (All + * interrupt entries on x86_64 set SS to NULL.) We prevent that + * from happening by reloading SS in __switch_to. */ USERGS_SYSRET32 |