linux-kernel - Re: [PATCH] arch_check_bp_in_kernelspace: fix the range check

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Message-ID: <20121119174728.GA11365@redhat.com>
Date:	Mon, 19 Nov 2012 18:47:28 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	Amnon Shiloh <u3557@...o.sublimeip.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch_check_bp_in_kernelspace: fix the range check

On 11/09, Oleg Nesterov wrote:
>
> On 11/09, Oleg Nesterov wrote:
> >
> > Note: TASK_SIZE doesn't look right at least on x86, I think it should
> > be replaced by TASK_SIZE_MAX.
> > ...
> > --- x/arch/x86/kernel/hw_breakpoint.c
> > +++ x/arch/x86/kernel/hw_breakpoint.c
> > @@ -200,7 +200,7 @@ int arch_check_bp_in_kernelspace(struct
> >  	va = info->address;
> >  	len = get_hbp_len(info->len);
> >
> > -	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
> > +	return (va >= TASK_SIZE) || ((va + len - 1) >= TASK_SIZE);
>
> But actully I'd like to ask another question.
>
> Can't we add the additional !in_gate_area_no_mm() check to allow
> the hw breakpoints in vsyscall?
>
> Quoting Amnon:
>
> 	My service needs to catch the system-calls of its traced son.
> 	Almost all system-calls are caught with PTRACE_SYSCALL, but not those
> 	using the vsyscall page - especially "gettimeofday()" and "time()".
>
> 	...
>
> 	However, the code in "arch/x86/kernel/ptrace.c" forbids catching kernel
> 	addresses.
>
> I tend to agree with Amnon...
>
> What do you think?

ping ;)

I agree the patch I sent is very minor (although it looks like the trivial
bugfix to me).

Just I think Amnon has a point, shouldn't we change this change like below?
(on top of this fixlet).

Oleg.

--- x/arch/x86/kernel/hw_breakpoint.c
+++ x/arch/x86/kernel/hw_breakpoint.c
@@ -188,6 +188,11 @@ static int get_hbp_len(u8 hbp_len)
 	return len_in_bytes;
 }
 
+static inline bool bp_in_gate(unsigned long start, unsigned long end)
+{
+	return in_gate_area_no_mm(start) && in_gate_area_no_mm(end);
+}
+
 /*
  * Check for virtual address in kernel space.
  */
@@ -200,7 +205,8 @@ int arch_check_bp_in_kernelspace(struct 
 	va = info->address;
 	len = get_hbp_len(info->len);
 
-	return (va >= TASK_SIZE) || ((va + len - 1) >= TASK_SIZE);
+	return ((va >= TASK_SIZE) || ((va + len - 1) >= TASK_SIZE)) &&
+		!bp_in_gate(va, va + len - 1);
 }
 
 int arch_bp_generic_fields(int x86_len, int x86_type,

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