linux-kernel - Re: [PATCH] x86_64: test that userspace stack is in fact NX

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Message-ID: <ZRrBwwf4nUiTju8Z@gmail.com>
Date:   Mon, 2 Oct 2023 15:12:35 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86_64: test that userspace stack is in fact NX


* Alexey Dobriyan <adobriyan@...il.com> wrote:

> Here is how it works:
> 
> * fault and fill the stack from rsp with int3 down until rlimit allows,
> * fill upwards with int3 too, overwrite libc stuff, argv, envp,
> * try to exec int3 on each page and catch it with either SIGSEGV or
>   SIGTRAP handler.
> 
> Note: trying to execute _every_ int3 takes 30-40 seconds even on fast
> machine, so only 1 int3 per page is tried.
> 
> Tested on F37 kernel and on custom kernel which did
> 
> 	vm_flags |= VM_EXEC;
> 
> to stack VMA.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  tools/testing/selftests/x86/Makefile   |    3 
>  tools/testing/selftests/x86/nx_stack.c |  167 +++++++++++++++++++++++++++++++++
>  2 files changed, 170 insertions(+)

Ok, that's a good idea, but could the test case please output something
human-readable that indicates whether the test was a success or not?

A typical testcase output is like:

  kepler:~/tip/tools/testing/selftests/x86> ./sigaltstack_32 
  [RUN]	Test an alternate signal stack of sufficient size.
	Raise SIGALRM. It is expected to be delivered.
  [OK]	SIGALRM signal delivered.

Or:

  kepler:~/tip/tools/testing/selftests/x86> ./test_vsyscall_64 
  ...
  [OK]	vsyscalls are emulated (1 instructions in vsyscall page)
  ...

... where the 'OK' denotes success of a test.

The nx_stack testcase only outputs:

  stack min 00007fffd75b5000
  stack max 00007fffd7db5000

... with only the exit code denoting success/failure.

Thanks,

	Ingo