Re: [PATCH] ARM: mm: add testcases for RODATA

Mark Rutland
2017-01-18T14:38:17Z

On Wed, Jan 18, 2017 at 10:53:10PM +0900, Jinbum Park wrote:
> This patch adds testcases for the CONFIG_DEBUG_RODATA option.
> It's similar to x86's testcases.
> It tests read-only mapped data and page-size aligned rodata section.

I note that LKDTM already has a similar test (though it just has a raw
write, and will crash the kernel).

> + asm volatile(
> + "0: str %[zero], [%[rodata_test]]\n"
> + " mov %[rslt], %[zero]\n"
> + "1:\n"
> + ".pushsection .text.fixup,\"ax\"\n"
> + ".align 2\n"
> + "2:\n"
> + "b 1b\n"
> + ".popsection\n"
> + ".pushsection __ex_table,\"a\"\n"
> + ".align 3\n"
> + ".long 0b, 2b\n"
> + ".popsection\n"
> + : [rslt] "=r" (result)
> + : [zero] "r" (0UL), [rodata_test] "r" (&rodata_test_data)
> + );

This is the only architecture-specific part of the file.

Rather than duplicating the logic from x86, can't we use generic
infrastructure for this part, and move the existing test into a shared
location?

e.g. could we change to KERNEL_DS and use put_user here?

> + if (!result) {
> + pr_err("rodata_test: test data was not read only\n");
> + return -ENODEV;
> + }
> +
> + /* test 3: check the value hasn't changed */
> + /* If this test fails, we managed to overwrite the data */
> + if (!rodata_test_data) {
> + pr_err("rodata_test: Test 3 fails (end data)\n");
> + return -ENODEV;
> + }
> +
> + /* test 4: check if the rodata section is 4Kb aligned */
> + start = (unsigned long)__start_rodata;
> + end = (unsigned long)__end_rodata;
> + if (start & (PAGE_SIZE - 1)) {
> + pr_err("rodata_test: .rodata is not 4k aligned\n");
> + return -ENODEV;
> + }
> + if (end & (PAGE_SIZE - 1)) {
> + pr_err("rodata_test: .rodata end is not 4k aligned\n");
> + return -ENODEV;
> + }

s/4k/page/ in the prints, if this becomes generic.

Thanks,
Mark.