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* [PATCH] x86/entry/64/paravirt: Use paravirt-safe macro to access eflags
@ 2017-11-27 18:05 Boris Ostrovsky
  0 siblings, 0 replies; 3+ messages in thread
From: Boris Ostrovsky @ 2017-11-27 18:05 UTC (permalink / raw)
  To: linux-kernel, xen-devel; +Cc: jgross, x86, mingo, luto, hpa, tglx

Commit 1d3e53e8624a ("x86/entry/64: Refactor IRQ stacks and make
them NMI-safe") added DEBUG_ENTRY_ASSERT_IRQS_OFF macro that acceses
eflags using 'pushfq' instruction when testing for IF bit. On PV Xen
guests looking at IF flag directly will always see it set, resulting
in 'ud2'.

Introduce SAVE_FLAGS() macro that will use appropriate save_fl pv op
when running paravirt.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/entry/entry_64.S        |    5 ++---
 arch/x86/include/asm/irqflags.h  |    3 +++
 arch/x86/include/asm/paravirt.h  |    9 +++++++++
 arch/x86/kernel/asm-offsets_64.c |    3 +++
 4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f81d50d..4bb7719 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -466,12 +466,11 @@ END(irq_entries_start)
 
 .macro DEBUG_ENTRY_ASSERT_IRQS_OFF
 #ifdef CONFIG_DEBUG_ENTRY
-	pushfq
-	testl $X86_EFLAGS_IF, (%rsp)
+	SAVE_FLAGS(CLBR_ANY)
+	testl $X86_EFLAGS_IF, %eax
 	jz .Lokay_\@
 	ud2
 .Lokay_\@:
-	addq $8, %rsp
 #endif
 .endm
 
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index c8ef23f..7f65f3f 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -142,6 +142,9 @@ static inline notrace unsigned long arch_local_irq_save(void)
 	swapgs;					\
 	sysretl
 
+#ifdef CONFIG_DEBUG_ENTRY
+#define SAVE_FLAGS(x)		pushfq
+#endif
 #else
 #define INTERRUPT_RETURN		iret
 #define ENABLE_INTERRUPTS_SYSEXIT	sti; sysexit
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 283efca..892df37 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -927,6 +927,15 @@ static inline notrace unsigned long arch_local_irq_save(void)
 	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret64),	\
 		  CLBR_NONE,						\
 		  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret64))
+
+#ifdef CONFIG_DEBUG_ENTRY
+#define SAVE_FLAGS(clobbers)                                        \
+	PARA_SITE(PARA_PATCH(pv_irq_ops, PV_IRQ_save_fl), clobbers, \
+		  PV_SAVE_REGS(clobbers | CLBR_CALLEE_SAVE);        \
+		  call PARA_INDIRECT(pv_irq_ops+PV_IRQ_save_fl);    \
+		  PV_RESTORE_REGS(clobbers | CLBR_CALLEE_SAVE);)
+#endif
+
 #endif	/* CONFIG_X86_32 */
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index 630212f..e3a5175 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -23,6 +23,9 @@ int main(void)
 #ifdef CONFIG_PARAVIRT
 	OFFSET(PV_CPU_usergs_sysret64, pv_cpu_ops, usergs_sysret64);
 	OFFSET(PV_CPU_swapgs, pv_cpu_ops, swapgs);
+#ifdef CONFIG_DEBUG_ENTRY
+	OFFSET(PV_IRQ_save_fl, pv_irq_ops, save_fl);
+#endif
 	BLANK();
 #endif
 
-- 
1.7.1


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^ permalink raw reply related	[flat|nested] 3+ messages in thread
* Re: [PATCH] x86/entry/64/paravirt: Use paravirt-safe macro to access eflags
       [not found] <1511805918-8041-1-git-send-email-boris.ostrovsky@oracle.com>
@ 2017-11-27 19:22 ` Juergen Gross
       [not found] ` <be726c34-865b-e238-9fa2-96d0df859e13@suse.com>
  1 sibling, 0 replies; 3+ messages in thread
From: Juergen Gross @ 2017-11-27 19:22 UTC (permalink / raw)
  To: Boris Ostrovsky, linux-kernel, xen-devel; +Cc: tglx, mingo, x86, luto, hpa

On 27/11/17 19:05, Boris Ostrovsky wrote:
> Commit 1d3e53e8624a ("x86/entry/64: Refactor IRQ stacks and make
> them NMI-safe") added DEBUG_ENTRY_ASSERT_IRQS_OFF macro that acceses
> eflags using 'pushfq' instruction when testing for IF bit. On PV Xen
> guests looking at IF flag directly will always see it set, resulting
> in 'ud2'.
> 
> Introduce SAVE_FLAGS() macro that will use appropriate save_fl pv op
> when running paravirt.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
>  arch/x86/entry/entry_64.S        |    5 ++---
>  arch/x86/include/asm/irqflags.h  |    3 +++
>  arch/x86/include/asm/paravirt.h  |    9 +++++++++
>  arch/x86/kernel/asm-offsets_64.c |    3 +++
>  4 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index f81d50d..4bb7719 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -466,12 +466,11 @@ END(irq_entries_start)
>  
>  .macro DEBUG_ENTRY_ASSERT_IRQS_OFF
>  #ifdef CONFIG_DEBUG_ENTRY
> -	pushfq
> -	testl $X86_EFLAGS_IF, (%rsp)
> +	SAVE_FLAGS(CLBR_ANY)
> +	testl $X86_EFLAGS_IF, %eax

Are you sure %eax is allowed to be modified?

>  	jz .Lokay_\@
>  	ud2
>  .Lokay_\@:
> -	addq $8, %rsp
>  #endif
>  .endm
>  
> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
> index c8ef23f..7f65f3f 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -142,6 +142,9 @@ static inline notrace unsigned long arch_local_irq_save(void)
>  	swapgs;					\
>  	sysretl
>  
> +#ifdef CONFIG_DEBUG_ENTRY
> +#define SAVE_FLAGS(x)		pushfq

Isn't there a "pop %rax" missing (assuming %rax is allowed to be
modified) ?


Juergen

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^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: [PATCH] x86/entry/64/paravirt: Use paravirt-safe macro to access eflags
       [not found] ` <be726c34-865b-e238-9fa2-96d0df859e13@suse.com>
@ 2017-11-27 21:40   ` Boris Ostrovsky
  0 siblings, 0 replies; 3+ messages in thread
From: Boris Ostrovsky @ 2017-11-27 21:40 UTC (permalink / raw)
  To: Juergen Gross, linux-kernel, xen-devel; +Cc: tglx, mingo, x86, luto, hpa

On 11/27/2017 02:22 PM, Juergen Gross wrote:
> On 27/11/17 19:05, Boris Ostrovsky wrote:
>> Commit 1d3e53e8624a ("x86/entry/64: Refactor IRQ stacks and make
>> them NMI-safe") added DEBUG_ENTRY_ASSERT_IRQS_OFF macro that acceses
>> eflags using 'pushfq' instruction when testing for IF bit. On PV Xen
>> guests looking at IF flag directly will always see it set, resulting
>> in 'ud2'.
>>
>> Introduce SAVE_FLAGS() macro that will use appropriate save_fl pv op
>> when running paravirt.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>  arch/x86/entry/entry_64.S        |    5 ++---
>>  arch/x86/include/asm/irqflags.h  |    3 +++
>>  arch/x86/include/asm/paravirt.h  |    9 +++++++++
>>  arch/x86/kernel/asm-offsets_64.c |    3 +++
>>  4 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> index f81d50d..4bb7719 100644
>> --- a/arch/x86/entry/entry_64.S
>> +++ b/arch/x86/entry/entry_64.S
>> @@ -466,12 +466,11 @@ END(irq_entries_start)
>>  
>>  .macro DEBUG_ENTRY_ASSERT_IRQS_OFF
>>  #ifdef CONFIG_DEBUG_ENTRY
>> -	pushfq
>> -	testl $X86_EFLAGS_IF, (%rsp)
>> +	SAVE_FLAGS(CLBR_ANY)
>> +	testl $X86_EFLAGS_IF, %eax
> Are you sure %eax is allowed to be modified?
>
>>  	jz .Lokay_\@
>>  	ud2
>>  .Lokay_\@:
>> -	addq $8, %rsp
>>  #endif
>>  .endm
>>  
>> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
>> index c8ef23f..7f65f3f 100644
>> --- a/arch/x86/include/asm/irqflags.h
>> +++ b/arch/x86/include/asm/irqflags.h
>> @@ -142,6 +142,9 @@ static inline notrace unsigned long arch_local_irq_save(void)
>>  	swapgs;					\
>>  	sysretl
>>  
>> +#ifdef CONFIG_DEBUG_ENTRY
>> +#define SAVE_FLAGS(x)		pushfq
> Isn't there a "pop %rax" missing (assuming %rax is allowed to be
> modified) ?


Yes to both. Need to save %rax in DEBUG_ENTRY_ASSERT_IRQS_OFF.

Thanks.
-boris

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^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-11-27 21:40 UTC | newest]

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2017-11-27 19:22 ` [PATCH] x86/entry/64/paravirt: Use paravirt-safe macro to access eflags Juergen Gross
     [not found] ` <be726c34-865b-e238-9fa2-96d0df859e13@suse.com>
2017-11-27 21:40   ` Boris Ostrovsky
2017-11-27 18:05 Boris Ostrovsky

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