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Date:   Tue, 3 Oct 2023 16:03:55 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] x86_64: test that userspace stack is in fact NX
Message-ID: <8b1297a4-00f0-431a-8fff-4ce2745adfab@p183>
References: <4b78a714-5ac3-4783-8256-1dda4673db01@p183>
 <ZRrBwwf4nUiTju8Z@gmail.com>
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On Mon, Oct 02, 2023 at 03:12:35PM +0200, Ingo Molnar wrote:
> 
> * Alexey Dobriyan <adobriyan@gmail.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@gmail.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.

The way Unix Founding Fathers intented! :-)
OK, I'll add something.