Re: [PATCH 4.4 076/134] kprobes/x86: Set kprobes pages read-only

[Ben Hutchings <ben.hutchings@codethink.co.uk>]

On Mon, 2018-03-19 at 19:05 +0100, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Masami Hiramatsu <mhiramat@kernel.org>
> 
> 
> [ Upstream commit d0381c81c2f782fa2131178d11e0cfb23d50d631 ]

This caused a regression in mainline, fixed by:

commit c93f5cf571e7795f97d49ef51b766cf25e328545
Author: Masami Hiramatsu <mhiramat@kernel.org>
Date:   Thu May 25 19:38:17 2017 +0900

    kprobes/x86: Fix to set RWX bits correctly before releasing trampoline

Ben.

> Set the pages which is used for kprobes' singlestep buffer
> and optprobe's trampoline instruction buffer to readonly.
> This can prevent unexpected (or unintended) instruction
> modification.
> 
> This also passes rodata_test as below.
> 
> Without this patch, rodata_test shows a warning:
> 
>   WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:235 note_page+0x7a9/0xa20
>   x86/mm: Found insecure W+X mapping at address ffffffffa0000000/0xffffffffa0000000
> 
> With this fix, no W+X pages are found:
> 
>   x86/mm: Checked W+X mappings: passed, no W+X pages found.
>   rodata_test: all tests were successful
> 
> Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Brian Gerst <brgerst@gmail.com>
> Cc: David S . Miller <davem@davemloft.net>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ye Xiaolong <xiaolong.ye@intel.com>
> Link: http://lkml.kernel.org/r/149076375592.22469.14174394514338612247.stgit@devbox
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/x86/kernel/kprobes/core.c |    4 ++++
>  arch/x86/kernel/kprobes/opt.c  |    3 +++
>  2 files changed, 7 insertions(+)
> 
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -406,6 +406,8 @@ static int arch_copy_kprobe(struct kprob
>  {
>  	int ret;
>  
> +	set_memory_rw((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
> +
>  	/* Copy an instruction with recovering if other optprobe modifies it.*/
>  	ret = __copy_instruction(p->ainsn.insn, p->addr);
>  	if (!ret)
> @@ -420,6 +422,8 @@ static int arch_copy_kprobe(struct kprob
>  	else
>  		p->ainsn.boostable = -1;
>  
> +	set_memory_ro((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
> +
>  	/* Check whether the instruction modifies Interrupt Flag or not */
>  	p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn);
>  
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -370,6 +370,7 @@ int arch_prepare_optimized_kprobe(struct
>  	}
>  
>  	buf = (u8 *)op->optinsn.insn;
> +	set_memory_rw((unsigned long)buf & PAGE_MASK, 1);
>  
>  	/* Copy instructions into the out-of-line buffer */
>  	ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
> @@ -392,6 +393,8 @@ int arch_prepare_optimized_kprobe(struct
>  	synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
>  			   (u8 *)op->kp.addr + op->optinsn.size);
>  
> +	set_memory_ro((unsigned long)buf & PAGE_MASK, 1);
> +
>  	flush_icache_range((unsigned long) buf,
>  			   (unsigned long) buf + TMPL_END_IDX +
>  			   op->optinsn.size + RELATIVEJUMP_SIZE);

-- 
Ben Hutchings
Software Developer, Codethink Ltd.