[3.13.y-ckt stable] Patch "x86/asm/entry/64: Remove a bogus 'ret_from_fork' optimization" has been added to staging queue
Kamal Mostafa
kamal at canonical.com
Mon Apr 6 21:58:06 UTC 2015
This is a note to let you know that I have just added a patch titled
x86/asm/entry/64: Remove a bogus 'ret_from_fork' optimization
to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue
This patch is scheduled to be released in version 3.13.11-ckt19.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From 0a0cdf2ceed9e58a91d61eb9cf6f079d9380bb8c Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto at amacapital.net>
Date: Thu, 5 Mar 2015 01:09:44 +0100
Subject: 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 <luto at amacapital.net>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Denys Vlasenko <dvlasenk at redhat.com>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Oleg Nesterov <oleg at redhat.com>
Cc: Thomas Gleixner <tglx at 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 at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.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 3d47217..082d3ce 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -579,11 +579,14 @@ 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
--
1.9.1
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