On 04/26, Oleg Nesterov wrote:
> On 04/26, H. Peter Anvin wrote:
> >
> > On 04/26/2013 09:38 AM, Oleg Nesterov wrote:
> > >
> > > - do_debug:
> > >
> > > dr6 &= ~DR6_RESERVED;
> > >
> > > this also wrongly clears 32-63 bits. Fortunately these
> > > bits are reserved and must be zero.
> >
> > I don't think this is wrongly at all.
>
> OK, I meant that it also clears the bits that are not specified in
> DR6_RESERVED mask.
>
> > The whole point is to mask out
> > the bits that the handler doesn't want to deal with, so masking out the
> > reserved bits [63:32] seems reasonable to me.
>
> Then we should do
>
> - #define DR6_RESERVED 0xFFFF0FF0
> + #define DR6_RESERVED 0xFFFFFFFFFFFF0FF0
>
> ?
>
> or what? (just in case, I will happily agree with "do nothing" ;)
Or we can do the s/reserved/mask/ change and avoid any "unexpected"
effect of "long &= ~int". This allso allows to kill ifdef(__i386__).
But this is include/uapi, I do not know if I can simply remove the
old define's.
In short: whatever you prefer, including "leave it alone".
Oleg.
diff --git a/arch/x86/include/uapi/asm/debugreg.h
b/arch/x86/include/uapi/asm/debugreg.h
index 3c0874d..2678b23 100644
--- a/arch/x86/include/uapi/asm/debugreg.h
+++ b/arch/x86/include/uapi/asm/debugreg.h
@@ -14,8 +14,7 @@
which debugging register was responsible for the trap. The other bits
are either reserved or not of interest to us. */
-/* Define reserved bits in DR6 which are always set to 1 */
-#define DR6_RESERVED (0xFFFF0FF0)
+#define DR6_MASK (0xF00FU) /* Everything else is reserved */
#define DR_TRAP0 (0x1) /* db0 */
#define DR_TRAP1 (0x2) /* db1 */
@@ -32,6 +31,8 @@
and indicates what types of access we trap on, and how large the data
field is that we are looking at */
+#define DR_CONTROL_MASK (0xFFFF03FFU) /* Everything else is reserved */
+
#define DR_CONTROL_SHIFT 16 /* Skip this many bits in ctl register */
#define DR_CONTROL_SIZE 4 /* 4 control bits per register */
@@ -64,12 +65,6 @@
We can slow the instruction pipeline for instructions coming via the
gdt or the ldt if we want to. I am not sure why this is an advantage */
-#ifdef __i386__
-#define DR_CONTROL_RESERVED (0xFC00) /* Reserved by Intel */
-#else
-#define DR_CONTROL_RESERVED (0xFFFFFFFF0000FC00UL) /* Reserved */
-#endif
-
#define DR_LOCAL_SLOWDOWN (0x100) /* Local slow the pipeline */
#define DR_GLOBAL_SLOWDOWN (0x200) /* Global slow the pipeline */
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 7461f50..bc5fb98 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -657,7 +657,7 @@ static int ptrace_write_dr7(struct task_struct *tsk,
unsigned long data)
bool second_pass = false;
int i, rc, ret = 0;
- data &= ~DR_CONTROL_RESERVED;
+ data &= DR_CONTROL_MASK;
old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
restore:
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 68bda7a..42a635f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -402,7 +402,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs,
long error_code)
get_debugreg(dr6, 6);
/* Filter out all the reserved bits which are preset to 1 */
- dr6 &= ~DR6_RESERVED;
+ dr6 &= DR6_MASK;
/*
* If dr6 has no reason to give us about the origin of this trap,
--
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