[patch] i386: entry.s::error_code is not safe for kprobes

[patch] i386: entry.s::error_code is not safe for kprobes

[Chuck Ebbert]

Because code marked unsafe for kprobes jumps directly to
entry.S::error_code, that must be marked unsafe as well.
The easiest way to do that is to move the page fault entry
point to just before error_code and let it inherit the same
section.

Also moved all the ".previous" asm directives for kprobes
sections to column 1 and removed ".text" from them.

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>

---

x86_64 also has this problem but I wasn't sure whether to move
error_entry into .kprobes.text or convert offendors to the
"paranoid" infrastructure.

 arch/i386/kernel/entry.S |   25 +++++++++++++------------
 1 files changed, 13 insertions(+), 12 deletions(-)

--- 2.6.18-rc3-nb.orig/arch/i386/kernel/entry.S
+++ 2.6.18-rc3-nb/arch/i386/kernel/entry.S
@@ -587,11 +587,9 @@ ENTRY(name)				\
 /* The include is where all of the SMP etc. interrupts come from */
 #include "entry_arch.h"
 
-ENTRY(divide_error)
-	RING0_INT_FRAME
-	pushl $0			# no error code
-	CFI_ADJUST_CFA_OFFSET 4
-	pushl $do_divide_error
+KPROBE_ENTRY(page_fault)
+	RING0_EC_FRAME
+	pushl $do_page_fault
 	CFI_ADJUST_CFA_OFFSET 4
 	ALIGN
 error_code:
@@ -641,6 +639,7 @@ error_code:
 	call *%edi
 	jmp ret_from_exception
 	CFI_ENDPROC
+.previous
 
 ENTRY(coprocessor_error)
 	RING0_INT_FRAME
@@ -716,7 +715,8 @@ debug_stack_correct:
 	call do_debug
 	jmp ret_from_exception
 	CFI_ENDPROC
-	.previous .text
+.previous
+
 /*
  * NMI is doubly nasty. It can happen _while_ we're handling
  * a debug fault, and the debug fault hasn't yet been able to
@@ -812,7 +812,7 @@ KPROBE_ENTRY(int3)
 	call do_int3
 	jmp ret_from_exception
 	CFI_ENDPROC
-	.previous .text
+.previous
 
 ENTRY(overflow)
 	RING0_INT_FRAME
@@ -877,7 +877,7 @@ KPROBE_ENTRY(general_protection)
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp error_code
 	CFI_ENDPROC
-	.previous .text
+.previous
 
 ENTRY(alignment_check)
 	RING0_EC_FRAME
@@ -886,13 +886,14 @@ ENTRY(alignment_check)
 	jmp error_code
 	CFI_ENDPROC
 
-KPROBE_ENTRY(page_fault)
-	RING0_EC_FRAME
-	pushl $do_page_fault
+ENTRY(divide_error)
+	RING0_INT_FRAME
+	pushl $0			# no error code
+	CFI_ADJUST_CFA_OFFSET 4
+	pushl $do_divide_error
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp error_code
 	CFI_ENDPROC
-	.previous .text
 
 #ifdef CONFIG_X86_MCE
 ENTRY(machine_check)
-- 
Chuck

Re: [patch] i386: entry.s::error_code is not safe for kprobes

[Andi Kleen]

On Thursday 03 August 2006 12:20, Chuck Ebbert wrote:
> Because code marked unsafe for kprobes jumps directly to
> entry.S::error_code, that must be marked unsafe as well.
> The easiest way to do that is to move the page fault entry
> point to just before error_code and let it inherit the same
> section.
> 
> Also moved all the ".previous" asm directives for kprobes
> sections to column 1 and removed ".text" from them.

Ok added thanks

-Andi

Re: [patch] i386: entry.s::error_code is not safe for kprobes

[S. P. Prasanna]

Hi Chuck,

Thanks for fixing the problem. Patch looks good to me.
I will make those changes for x86_64.

Thanks
Prasanna

On Thu, Aug 03, 2006 at 06:20:19AM -0400, Chuck Ebbert wrote:
> Because code marked unsafe for kprobes jumps directly to
> entry.S::error_code, that must be marked unsafe as well.
> The easiest way to do that is to move the page fault entry
> point to just before error_code and let it inherit the same
> section.
> 
> Also moved all the ".previous" asm directives for kprobes
> sections to column 1 and removed ".text" from them.
> 
> Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
> 
> ---
> 
> x86_64 also has this problem but I wasn't sure whether to move
> error_entry into .kprobes.text or convert offendors to the
> "paranoid" infrastructure.
> 
>  arch/i386/kernel/entry.S |   25 +++++++++++++------------
>  1 files changed, 13 insertions(+), 12 deletions(-)
> 
> --- 2.6.18-rc3-nb.orig/arch/i386/kernel/entry.S
> +++ 2.6.18-rc3-nb/arch/i386/kernel/entry.S
> @@ -587,11 +587,9 @@ ENTRY(name)				\
>  /* The include is where all of the SMP etc. interrupts come from */
>  #include "entry_arch.h"
>  
> -ENTRY(divide_error)
> -	RING0_INT_FRAME
> -	pushl $0			# no error code
> -	CFI_ADJUST_CFA_OFFSET 4
> -	pushl $do_divide_error
> +KPROBE_ENTRY(page_fault)
> +	RING0_EC_FRAME
> +	pushl $do_page_fault
>  	CFI_ADJUST_CFA_OFFSET 4
>  	ALIGN
>  error_code:
> @@ -641,6 +639,7 @@ error_code:
>  	call *%edi
>  	jmp ret_from_exception
>  	CFI_ENDPROC
> +.previous
>  
>  ENTRY(coprocessor_error)
>  	RING0_INT_FRAME
> @@ -716,7 +715,8 @@ debug_stack_correct:
>  	call do_debug
>  	jmp ret_from_exception
>  	CFI_ENDPROC
> -	.previous .text
> +.previous
> +
>  /*
>   * NMI is doubly nasty. It can happen _while_ we're handling
>   * a debug fault, and the debug fault hasn't yet been able to
> @@ -812,7 +812,7 @@ KPROBE_ENTRY(int3)
>  	call do_int3
>  	jmp ret_from_exception
>  	CFI_ENDPROC
> -	.previous .text
> +.previous
>  
>  ENTRY(overflow)
>  	RING0_INT_FRAME
> @@ -877,7 +877,7 @@ KPROBE_ENTRY(general_protection)
>  	CFI_ADJUST_CFA_OFFSET 4
>  	jmp error_code
>  	CFI_ENDPROC
> -	.previous .text
> +.previous
>  
>  ENTRY(alignment_check)
>  	RING0_EC_FRAME
> @@ -886,13 +886,14 @@ ENTRY(alignment_check)
>  	jmp error_code
>  	CFI_ENDPROC
>  
> -KPROBE_ENTRY(page_fault)
> -	RING0_EC_FRAME
> -	pushl $do_page_fault
> +ENTRY(divide_error)
> +	RING0_INT_FRAME
> +	pushl $0			# no error code
> +	CFI_ADJUST_CFA_OFFSET 4
> +	pushl $do_divide_error
>  	CFI_ADJUST_CFA_OFFSET 4
>  	jmp error_code
>  	CFI_ENDPROC
> -	.previous .text
>  
>  #ifdef CONFIG_X86_MCE
>  ENTRY(machine_check)
> -- 
> Chuck

-- 
S.P. Prasanna
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@in.ibm.com
Ph: 91-80-41776329