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Date: Thu, 19 Jan 2017 15:57:01 +0000
From: Mark Rutland <mark.rutland@....com>
To: Jinbum Park <jinb.park7@...il.com>
Cc: tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org,
keescook@...omium.org, arjan@...ux.intel.com,
akpm@...uxfoundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, labbott@...hat.com,
kernel-hardening@...ts.openwall.com,
kernel-janitors@...r.kernel.org, linux@...linux.org.uk
Subject: Re: [PATCH] mm: add arch-independent testcases for RODATA
On Thu, Jan 19, 2017 at 11:51:14PM +0900, Jinbum Park wrote:
> This patch adds arch-independent testcases for RODATA.
> Both x86 and x86_64 already have testcases for RODATA,
> But they are arch-specific because using inline assembly directly.
>
> and cacheflush.h is not suitable location for rodata-test related things.
> Since they were in cacheflush.h,
> If someone change the state of CONFIG_DEBUG_RODATA_TEST,
> It cause overhead of kernel build.
>
> To solve above issue,
> write arch-independent testcases and move it to shared location. (main.c)
This is clearly a rework and move of the existing x86 test, and not the
addition of a completely new test (see Arjan's comment about his credit
being removed...).
I would recommend that you turn this into a series that makes the x86
code generic, then moves it out into a common location where it can be
used by others. e.g.
1) make the test use put_user()
2) move the rodata_test() call and the prototype to a common location
3) move the test out to mm/ (with no changes to the file itself)
Otherwise, comments below.
> diff --git a/mm/rodata_test.c b/mm/rodata_test.c
> new file mode 100644
> index 0000000..d5b0504
> --- /dev/null
> +++ b/mm/rodata_test.c
> @@ -0,0 +1,63 @@
> +/*
> + * rodata_test.c: functional test for mark_rodata_ro function
> + *
> + * (C) Copyright 2017 Jinbum Park <jinb.park7@...il.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; version 2
> + * of the License.
> + */
> +#include <asm/uaccess.h>
> +#include <asm/sections.h>
> +
> +const int rodata_test_data = 0xC3;
> +EXPORT_SYMBOL_GPL(rodata_test_data);
> +
> +void rodata_test(void)
> +{
> + unsigned long start, end, rodata_addr;
> + int zero = 0;
> +
> + /* prepare test */
> + rodata_addr = ((unsigned long)&rodata_test_data);
> +
> + /* test 1: read the value */
> + /* If this test fails, some previous testrun has clobbered the state */
> + if (!rodata_test_data) {
> + pr_err("rodata_test: test 1 fails (start data)\n");
> + return;
> + }
> +
> + /* test 2: write to the variable; this should fault */
> + /*
> + * This must be written in assembly to be able to catch the
> + * exception that is supposed to happen in the correct case.
> + *
> + * So that put_user macro is used to write arch-independent assembly.
> + */
> + if (!put_user(zero, (int *)rodata_addr)) {
> + pr_err("rodata_test: test data was not read only\n");
> + return;
> + }
As I mentioned in the original posting, you need to change to KERNEL_DS
for the put_user.
Russell's suggestion to use probe_kernel_write() is strictly better;
please do that instead.
Thanks,
Mark.
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