From: Andy Lutomirski <luto@xxxxxxxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 956421fbb74c3a6261903f3836c0740187cf038b upstream. 'ret_from_fork' checks TIF_IA32 to determine whether 'pt_regs' and the related state make sense for 'ret_from_sys_call'. This is entirely the wrong check. TS_COMPAT would make a little more sense, but there's really no point in keeping this optimization at all. This fixes a return to the wrong user CS if we came from int 0x80 in a 64-bit task. Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/4710be56d76ef994ddf59087aad98c000fbab9a4.1424989793.git.luto@xxxxxxxxxxxxxx [ Backported from tip:x86/asm. ] Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- arch/x86/kernel/entry_64.S | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index e96560628571..7b22af265d12 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -542,11 +542,14 @@ ENTRY(ret_from_fork) testl $3, CS-ARGOFFSET(%rsp) # from kernel_thread? jz 1f - testl $_TIF_IA32, TI_flags(%rcx) # 32-bit compat task needs IRET - jnz int_ret_from_sys_call - - RESTORE_TOP_OF_STACK %rdi, -ARGOFFSET - jmp ret_from_sys_call # go to the SYSRET fastpath + /* + * By the time we get here, we have no idea whether our pt_regs, + * ti flags, and ti status came from the 64-bit SYSCALL fast path, + * the slow path, or one of the ia32entry paths. + * Use int_ret_from_sys_call to return, since it can safely handle + * all of the above. + */ + jmp int_ret_from_sys_call 1: subq $REST_SKIP, %rsp # leave space for volatiles -- 2.3.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html