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 <email@example.com>
Cc: Peter Anvin <firstname.lastname@example.org>
Cc: Borislav Petkov <email@example.com>
Cc: Denys Vlasenko <firstname.lastname@example.org>
Cc: Brian Gerst <email@example.com>
Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
5 files changed