* Remove __end_entry_SYSENTER_compat?
@ 2017-07-12 4:13 Borislav Petkov
2017-07-12 8:48 ` Ingo Molnar
0 siblings, 1 reply; 3+ messages in thread
From: Borislav Petkov @ 2017-07-12 4:13 UTC (permalink / raw)
To: Andy Lutomirski; +Cc: x86-ml, lkml
Anyone think this is an OK-ish idea?
It saves us the global symbol but requires the two functions to remained
glued together. :-\
---
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index e1721dafbcb1..262519da8661 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -131,7 +131,6 @@ ENTRY(entry_SYSENTER_compat)
pushq $X86_EFLAGS_FIXED
popfq
jmp .Lsysenter_flags_fixed
-GLOBAL(__end_entry_SYSENTER_compat)
ENDPROC(entry_SYSENTER_compat)
/*
@@ -180,6 +179,9 @@ ENDPROC(entry_SYSENTER_compat)
* edi arg5
* esp user stack
* 0(%esp) arg6
+ *
+ * DO NOT! move this function and the above before adjusting
+ * is_sysenter_singlestep().
*/
ENTRY(entry_SYSCALL_compat)
/* Interrupts are off on entry. */
diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h
index 8d3964fc5f91..afdef9f3f0f0 100644
--- a/arch/x86/include/asm/proto.h
+++ b/arch/x86/include/asm/proto.h
@@ -21,7 +21,6 @@ void __end_SYSENTER_singlestep_region(void);
#ifdef CONFIG_IA32_EMULATION
void entry_SYSENTER_compat(void);
-void __end_entry_SYSENTER_compat(void);
void entry_SYSCALL_compat(void);
void entry_INT80_compat(void);
#endif
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bf54309b85da..143902ffe9ff 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -668,7 +668,7 @@ static bool is_sysenter_singlestep(struct pt_regs *regs)
(unsigned long)__begin_SYSENTER_singlestep_region;
#elif defined(CONFIG_IA32_EMULATION)
return (regs->ip - (unsigned long)entry_SYSENTER_compat) <
- (unsigned long)__end_entry_SYSENTER_compat -
+ (unsigned long)entry_SYSCALL_compat -
(unsigned long)entry_SYSENTER_compat;
#else
return false;
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: Remove __end_entry_SYSENTER_compat?
2017-07-12 4:13 Remove __end_entry_SYSENTER_compat? Borislav Petkov
@ 2017-07-12 8:48 ` Ingo Molnar
2017-07-12 9:25 ` Borislav Petkov
0 siblings, 1 reply; 3+ messages in thread
From: Ingo Molnar @ 2017-07-12 8:48 UTC (permalink / raw)
To: Borislav Petkov
Cc: Andy Lutomirski, x86-ml, lkml, Thomas Gleixner, H. Peter Anvin
* Borislav Petkov <bp@alien8.de> wrote:
> Anyone think this is an OK-ish idea?
>
> It saves us the global symbol but requires the two functions to remained
> glued together. :-\
>
> ---
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index e1721dafbcb1..262519da8661 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -131,7 +131,6 @@ ENTRY(entry_SYSENTER_compat)
> pushq $X86_EFLAGS_FIXED
> popfq
> jmp .Lsysenter_flags_fixed
> -GLOBAL(__end_entry_SYSENTER_compat)
> ENDPROC(entry_SYSENTER_compat)
>
> /*
> @@ -180,6 +179,9 @@ ENDPROC(entry_SYSENTER_compat)
> * edi arg5
> * esp user stack
> * 0(%esp) arg6
> + *
> + * DO NOT! move this function and the above before adjusting
> + * is_sysenter_singlestep().
> */
> ENTRY(entry_SYSCALL_compat)
> /* Interrupts are off on entry. */
> diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h
> index 8d3964fc5f91..afdef9f3f0f0 100644
> --- a/arch/x86/include/asm/proto.h
> +++ b/arch/x86/include/asm/proto.h
> @@ -21,7 +21,6 @@ void __end_SYSENTER_singlestep_region(void);
>
> #ifdef CONFIG_IA32_EMULATION
> void entry_SYSENTER_compat(void);
> -void __end_entry_SYSENTER_compat(void);
> void entry_SYSCALL_compat(void);
> void entry_INT80_compat(void);
> #endif
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index bf54309b85da..143902ffe9ff 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -668,7 +668,7 @@ static bool is_sysenter_singlestep(struct pt_regs *regs)
> (unsigned long)__begin_SYSENTER_singlestep_region;
> #elif defined(CONFIG_IA32_EMULATION)
> return (regs->ip - (unsigned long)entry_SYSENTER_compat) <
> - (unsigned long)__end_entry_SYSENTER_compat -
> + (unsigned long)entry_SYSCALL_compat -
> (unsigned long)entry_SYSENTER_compat;
> #else
> return false;
Hm, I'd argue that the old code is much clearer: we need both the start and the
end of a function and have the properly named symbols for that.
That entry_SYSCALL_compat() happens to start just where
__end_entry_SYSENTER_compat is an accident of placement.
Is it even true - doesn't ENTRY() imply an .align, in which case it might be that
__end_entry_SYSENTER_compat != entry_SYSCALL_compat?
In fact that appears to be the case for my defconfig:
ffffffff81942f90 T entry_SYSENTER_compat
ffffffff81942feb T __end_entry_SYSENTER_compat
ffffffff81942ff0 T entry_SYSCALL_compat
So unless there's some disadvantage beyond having one more symbol, I'd favor the
old approach.
Thanks,
Ingo
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Remove __end_entry_SYSENTER_compat?
2017-07-12 8:48 ` Ingo Molnar
@ 2017-07-12 9:25 ` Borislav Petkov
0 siblings, 0 replies; 3+ messages in thread
From: Borislav Petkov @ 2017-07-12 9:25 UTC (permalink / raw)
To: Ingo Molnar
Cc: Andy Lutomirski, x86-ml, lkml, Thomas Gleixner, H. Peter Anvin
On Wed, Jul 12, 2017 at 10:48:03AM +0200, Ingo Molnar wrote:
> Hm, I'd argue that the old code is much clearer: we need both the start and the
> end of a function and have the properly named symbols for that.
>
> That entry_SYSCALL_compat() happens to start just where
> __end_entry_SYSENTER_compat is an accident of placement.
Yeah, probably not worth the effort of actually making it less reliable
this way...
> Is it even true - doesn't ENTRY() imply an .align, in which case it might be that
> __end_entry_SYSENTER_compat != entry_SYSCALL_compat?
Yes, ENTRY does .p2align:
.globl __end_entry_SYSENTER_compat; __end_entry_SYSENTER_compat:
.type entry_SYSENTER_compat, @function ; .size entry_SYSENTER_compat, .-entry_SYSENTER_compat
# 184 "arch/x86/entry/entry_64_compat.S"
.globl entry_SYSCALL_compat ; .p2align 4, 0x90 ; entry_SYSCALL_compat:
^^^^^^
Pads to an alignment of 4 with NOPs.
> In fact that appears to be the case for my defconfig:
>
> ffffffff81942f90 T entry_SYSENTER_compat
> ffffffff81942feb T __end_entry_SYSENTER_compat
> ffffffff81942ff0 T entry_SYSCALL_compat
>
> So unless there's some disadvantage beyond having one more symbol, I'd favor the
> old approach.
Yeah, my only concern was getting rid of the global symbol but it
doesn't work in this case.
Thanks.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-07-12 4:13 Remove __end_entry_SYSENTER_compat? Borislav Petkov
2017-07-12 8:48 ` Ingo Molnar
2017-07-12 9:25 ` Borislav Petkov
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