linux-kernel - Re: [PATCH] x86/ftrace: Make sure that ftrace trampolines are not RWX

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Date:   Thu, 25 May 2017 18:09:10 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/ftrace: Make sure that ftrace trampolines are not
 RWX

On Wed, 24 May 2017 18:25:47 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 24 May 2017 21:13:27 +0200 (CEST)
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> 
> > > Oops: 0003 [#1] SMP
> > > Modules linked in:
> > > CPU: 3 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc2-test+ #42
> > > Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6
> > > 02/22/2014 task: ffff8802153a8000 task.stack: ffffc90000c74000
> > > RIP: 0010:new_slab+0x1e8/0x2b4
> > > RSP: 0000:ffffc90000c77b28 EFLAGS: 00010282
> > > RAX: 0000000040040000 RBX: ffff880216003f00 RCX: ffff880214f5c058
> > > RDX: 0000000000000000 RSI: ffff880214f5c000 RDI: ffff880216003f00
> > > RBP: ffffc90000c77b70 R08: 000000000000002a R09: 0000000000000000
> > > R10: 00000000000201e2 R11: 0000000000020190 R12: ffff880214f5c000
> > > R13: 000000000000002e R14: 0000000000000001 R15: ffffea000853d700
> > > FS:  0000000000000000(0000) GS:ffff88021eb80000(0000)
> > > knlGS:0000000000000000 CS:  0010 DS: 0000 ES: 0000 CR0:
> > > 0000000080050033 CR2: ffff880214f5c000 CR3: 000000000221d000 CR4:
> > > 00000000001406e0 Call Trace:
> > >  ? interleave_nodes+0x29/0x40
> > >  ___slab_alloc+0x2e8/0x49e  
> > 
> > That does not make any sense, but I'm digging into it.
> 
> The trampolines uses the module allocation, and it appears, that needs
> to become rw before freeing again.

Oops, I also have to fix kprobes side, because it has same issue.

Thanks!

> 
> I applied this patch, and it appears to fix the bug for me.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> 
> -- Steve
> 
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 663a35d..5e93a9a 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -689,8 +689,12 @@ static inline void *alloc_tramp(unsigned long size)
>  {
>  	return module_alloc(size);
>  }
> -static inline void tramp_free(void *tramp)
> +static inline void tramp_free(void *tramp, int size)
>  {
> +	int npages;
> +
> +	npages = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +	set_memory_rw((unsigned long)tramp, npages);
>  	module_memfree(tramp);
>  }
>  #else
> @@ -699,7 +703,7 @@ static inline void *alloc_tramp(unsigned long size)
>  {
>  	return NULL;
>  }
> -static inline void tramp_free(void *tramp) { }
> +static inline void tramp_free(void *tramp, int size) { }
>  #endif
>  
>  /* Defined as markers to the end of the ftrace default trampolines */
> @@ -771,7 +775,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>  	/* Copy ftrace_caller onto the trampoline memory */
>  	ret = probe_kernel_read(trampoline, (void *)start_offset, size);
>  	if (WARN_ON(ret < 0)) {
> -		tramp_free(trampoline);
> +		tramp_free(trampoline, *tramp_size);
>  		return 0;
>  	}
>  
> @@ -797,7 +801,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>  
>  	/* Are we pointing to the reference? */
>  	if (WARN_ON(memcmp(op_ptr.op, op_ref, 3) != 0)) {
> -		tramp_free(trampoline);
> +		tramp_free(trampoline, *tramp_size);
>  		return 0;
>  	}
>  
> @@ -943,7 +947,7 @@ void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
>  	if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
>  		return;
>  
> -	tramp_free((void *)ops->trampoline);
> +	tramp_free((void *)ops->trampoline, ops->trampoline_size);
>  	ops->trampoline = 0;
>  }
>  


-- 
Masami Hiramatsu <mhiramat@...nel.org>