Re: [PATCH v2 8/8] selftests/x86: Add a test for process_vm_readv() on the vsyscall page

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:09PM -0700, Andy Lutomirski wrote:
> get_gate_page() is a piece of somewhat alarming code to make
> get_user_pages() work on the vsyscall page.  Test it via
> process_vm_readv().
> 
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  tools/testing/selftests/x86/test_vsyscall.c | 35 +++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
> index 34a1d35995ef..4602326b8f5b 100644
> --- a/tools/testing/selftests/x86/test_vsyscall.c
> +++ b/tools/testing/selftests/x86/test_vsyscall.c
> @@ -18,6 +18,7 @@
>  #include <sched.h>
>  #include <stdbool.h>
>  #include <setjmp.h>
> +#include <sys/uio.h>
>  
>  #ifdef __x86_64__
>  # define VSYS(x) (x)
> @@ -459,6 +460,38 @@ static int test_vsys_x(void)
>  	return 0;
>  }
>  
> +static int test_process_vm_readv(void)
> +{
> +#ifdef __x86_64__
> +	char buf[4096];
> +	struct iovec local, remote;
> +	int ret;
> +
> +	printf("[RUN]\tprocess_vm_readv() from vsyscall page\n");
> +
> +	local.iov_base = buf;
> +	local.iov_len = 4096;
> +	remote.iov_base = (void *)0xffffffffff600000;
> +	remote.iov_len = 4096;
> +	ret = process_vm_readv(getpid(), &local, 1, &remote, 1, 0);
> +	if (ret != 4096) {
> +		printf("[OK]\tprocess_vm_readv() failed (ret = %d, errno = %d)\n", ret, errno);
> +		return 0;
> +	}
> +
> +	if (vsyscall_map_r) {
> +		if (!memcmp(buf, (const void *)0xffffffffff600000, 4096)) {
> +			printf("[OK]\tIt worked and read correct data\n");
> +		} else {
> +			printf("[FAIL]\tIt worked but returned incorrect data\n");
> +			return 1;
> +		}
> +	}
> +#endif
> +
> +	return 0;
> +}
> +
>  #ifdef __x86_64__
>  #define X86_EFLAGS_TF (1UL << 8)
>  static volatile sig_atomic_t num_vsyscall_traps;
> @@ -533,6 +566,8 @@ int main(int argc, char **argv)
>  	nerrs += test_vsys_r();
>  	nerrs += test_vsys_x();
>  
> +	nerrs += test_process_vm_readv();
> +
>  #ifdef __x86_64__
>  	nerrs += test_emulation();
>  #endif
> -- 
> 2.21.0
> 

-- 
Kees Cook