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* Re: ptrace denies access to EFLAGS_RF
@ 2006-01-06  4:11 Chuck Ebbert
  2006-01-06  9:39 ` Stephane Eranian
  2006-01-06 14:02 ` Stephane Eranian
  0 siblings, 2 replies; 6+ messages in thread
From: Chuck Ebbert @ 2006-01-06  4:11 UTC (permalink / raw)
  To: Stephane Eranian; +Cc: linux-kernel, Linus Torvalds, Ingo Molnar, Andrew Morton

In-Reply-To: <20060105105130.GC3712@frankl.hpl.hp.com>

On Thu, 5 Jan 2006 at 02:51:30 -0800, Stephane Eranian wrote:

> I am trying to the user HW debug registers on i386
> and I am running into a problem with ptrace() not allowing access
> to EFLAGS_RF for POKEUSER (see FLAG_MASK).
> 
> I am not sure I understand the motivation for denying access
> to this flag which can be used to resume after a code
> breakpoint has been reached. It avoids the need to remove the
> breakpoint, single step, and reinstall. The equivalent
> functionality exists on IA-64 and is allowed by ptrace().

I see no reason for denying this.  This patch should fix it:


i386: PTRACE_POKEUSR: allow changing RF bit in EFLAGS register.

Setting RF (resume flag) allows a debugger to resume execution
after a code breakpoint without tripping the breakpoint again.
It is reset by the CPU after execution of one instruction.

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

--- 2.6.15a.orig/arch/i386/kernel/ptrace.c
+++ 2.6.15a/arch/i386/kernel/ptrace.c
@@ -32,9 +32,12 @@
  * in exit.c or in signal.c.
  */
 
-/* determines which flags the user has access to. */
-/* 1 = access 0 = no access */
-#define FLAG_MASK 0x00044dd5
+/*
+ * Determines which flags the user has access to [1 = access, 0 = no access].
+ * Prohibits changing ID(21), VIP(20), VIF(19), VM(17), IOPL(12-13), IF(9).
+ * Also masks reserved bits (31-22, 15, 5, 3, 1).
+ */
+#define FLAG_MASK 0x00054dd5
 
 /* set's the trap flag. */
 #define TRAP_FLAG 0x100
-- 
Chuck
Currently reading: _Thud!_ by Terry Pratchett

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: ptrace denies access to EFLAGS_RF
@ 2006-01-06 16:10 Chuck Ebbert
  2006-01-12 22:11 ` Stephane Eranian
  0 siblings, 1 reply; 6+ messages in thread
From: Chuck Ebbert @ 2006-01-06 16:10 UTC (permalink / raw)
  To: Stephane Eranian; +Cc: linux-kernel, Andi Kleen, discuss

In-Reply-To: <20060106140217.GD7676@frankl.hpl.hp.com>

On Fri, 6 Jan 2006 at 06:02:17 -0800, Stephane Eranian wrote:


> To my surprise, applying the same fix to the x86_64 does not
> solve the problem on my Opteron box. I verified that the
> offset (144) matches with what the kernel is expecting.
> Somehow the RF is lost or not set in the proper location.
> I cannot make forward progress once I reach the breakpoint.


I sent this to Andi this morning.  Does it work for you?

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

 arch/x86_64/ia32/ptrace32.c |    9 ++++++---
 arch/x86_64/kernel/ptrace.c |    9 ++++++---
 2 files changed, 12 insertions(+), 6 deletions(-)

--- 2.6.15-64a.orig/arch/x86_64/ia32/ptrace32.c
+++ 2.6.15-64a/arch/x86_64/ia32/ptrace32.c
@@ -28,9 +28,12 @@
 #include <asm/i387.h>
 #include <asm/fpu32.h>
 
-/* determines which flags the user has access to. */
-/* 1 = access 0 = no access */
-#define FLAG_MASK 0x44dd5UL
+/*
+ * Determines which flags the user has access to [1 = access, 0 = no access].
+ * Prohibits changing ID(21), VIP(20), VIF(19), VM(17), IOPL(12-13), IF(9).
+ * Also masks reserved bits (31-22, 15, 5, 3, 1).
+ */
+#define FLAG_MASK 0x54dd5UL
 
 #define R32(l,q) \
 	case offsetof(struct user32, regs.l): stack[offsetof(struct pt_regs, q)/8] = val; break
--- 2.6.15-64a.orig/arch/x86_64/kernel/ptrace.c
+++ 2.6.15-64a/arch/x86_64/kernel/ptrace.c
@@ -36,9 +36,12 @@
  * in exit.c or in signal.c.
  */
 
-/* determines which flags the user has access to. */
-/* 1 = access 0 = no access */
-#define FLAG_MASK 0x44dd5UL
+/*
+ * Determines which flags the user has access to [1 = access, 0 = no access].
+ * Prohibits changing ID(21), VIP(20), VIF(19), VM(17), IOPL(12-13), IF(9).
+ * Also masks reserved bits (63-22, 15, 5, 3, 1).
+ */
+#define FLAG_MASK 0x54dd5UL
 
 /* set's the trap flag. */
 #define TRAP_FLAG 0x100UL
-- 
Chuck
Currently reading: _Thud!_ by Terry Pratchett

^ permalink raw reply	[flat|nested] 6+ messages in thread
* ptrace denies access to EFLAGS_RF
@ 2006-01-05 10:51 Stephane Eranian
  0 siblings, 0 replies; 6+ messages in thread
From: Stephane Eranian @ 2006-01-05 10:51 UTC (permalink / raw)
  To: linux-kernel; +Cc: Stephane Eranian

Hello,

I am trying to the user HW debug registers on i386
and I am running into a problem with ptrace() not allowing access
to EFLAGS_RF for POKEUSER (see FLAG_MASK).

I am not sure I understand the motivation for denying access
to this flag which can be used to resume after a code
breakpoint has been reached. It avoids the need to remove the
breakpoint, single step, and reinstall. The equivalent
functionality exists on IA-64 and is allowed by ptrace().

Why is EFLAGS_RF not accessible to users on i386?

Thanks.

-- 
-Stephane

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2006-01-12 22:13 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2006-01-06  4:11 ptrace denies access to EFLAGS_RF Chuck Ebbert
2006-01-06  9:39 ` Stephane Eranian
2006-01-06 14:02 ` Stephane Eranian
  -- strict thread matches above, loose matches on Subject: below --
2006-01-06 16:10 Chuck Ebbert
2006-01-12 22:11 ` Stephane Eranian
2006-01-05 10:51 Stephane Eranian

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