• Andy Lutomirski's avatar
    x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue · 61f01dd9
    Andy Lutomirski authored
    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: e7d6eefa
    
     x86/vdso32/syscall.S: Do not load __USER32_DS to %ss
    Signed-off-by: default avatarAndy 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    61f01dd9