Messages in this thread Patch in this message | | | From | lizf@kernel ... | Subject | [PATCH 3.4 072/172] x86/asm/entry/64: Remove a bogus 'ret_from_fork' optimization | Date | Tue, 16 Jun 2015 16:35:26 +0800 |
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From: Andy Lutomirski <luto@amacapital.net>
3.4.108-rc1 review patch. If anyone has any objections, please let me know.
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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@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/4710be56d76ef994ddf59087aad98c000fbab9a4.1424989793.git.luto@amacapital.net [ Backported from tip:x86/asm. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Zefan Li <lizefan@huawei.com> --- 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 45f9c70..8b49131 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? jz retint_restore_args - 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) -- 1.9.1
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