From 159891c0953a89a28f793fc52373b031262c44d2 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 5 Mar 2015 01:09:44 +0100 Subject: [PATCH] x86/asm/entry/64: Remove a bogus 'ret_from_fork' optimization 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 Cc: Borislav Petkov Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/4710be56d76ef994ddf59087aad98c000fbab9a4.1424989793.git.luto@amacapital.net [ Backported from tip:x86/asm. ] Signed-off-by: Ingo Molnar Signed-off-by: Ben Hutchings --- 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 9d28dbacf8b7..8d15c698ef83 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -414,11 +414,14 @@ ENTRY(ret_from_fork) testl $3, CS-ARGOFFSET(%rsp) # from kernel_thread? je int_ret_from_sys_call - 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 CFI_ENDPROC END(ret_from_fork) -- 2.39.2