[LTP] [PATCH v2] syscalls/mprotect: align exec_func to 64 bytes
Daniel Mentz
danielmentz@google.com
Tue Feb 12 00:54:20 CET 2019
Two comments below. Otherwise, I'm fine with this. I reviewed this
patch and found it to be working on an aarch64 platform.
On Mon, Feb 11, 2019 at 2:15 PM Jan Stancek <jstancek@redhat.com> wrote:
>
> exec_func() is dummy/empty function. Try to align it so we don't
> need to worry about copying 2 pages. But also check that compiler
> aligned it and there's sufficient space between start of func_exec
> and end of page.
>
> This patch also removes copy_sz, which is now replaced with page_sz.
>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
> testcases/kernel/syscalls/mprotect/Makefile | 2 +
> testcases/kernel/syscalls/mprotect/mprotect04.c | 55 +++++++++++--------------
> 2 files changed, 27 insertions(+), 30 deletions(-)
>
> diff --git a/testcases/kernel/syscalls/mprotect/Makefile b/testcases/kernel/syscalls/mprotect/Makefile
> index bd617d806675..bc5c8bc10395 100644
> --- a/testcases/kernel/syscalls/mprotect/Makefile
> +++ b/testcases/kernel/syscalls/mprotect/Makefile
> @@ -20,4 +20,6 @@ top_srcdir ?= ../../../..
>
> include $(top_srcdir)/include/mk/testcases.mk
>
> +mprotect04: CFLAGS += -falign-functions=64
> +
> include $(top_srcdir)/include/mk/generic_leaf_target.mk
> diff --git a/testcases/kernel/syscalls/mprotect/mprotect04.c b/testcases/kernel/syscalls/mprotect/mprotect04.c
> index 60941a4220d5..0f7890dca03b 100644
> --- a/testcases/kernel/syscalls/mprotect/mprotect04.c
> +++ b/testcases/kernel/syscalls/mprotect/mprotect04.c
> @@ -55,7 +55,7 @@ int TST_TOTAL = ARRAY_SIZE(testfunc);
>
> static volatile int sig_caught;
> static sigjmp_buf env;
> -static unsigned int copy_sz;
> +static unsigned int page_sz;
> typedef void (*func_ptr_t)(void);
>
> int main(int ac, char **av)
> @@ -88,7 +88,7 @@ static void setup(void)
> {
> tst_tmpdir();
> tst_sig(NOFORK, sighandler, cleanup);
> - copy_sz = getpagesize() * 2;
> + page_sz = getpagesize();
>
> TEST_PAUSE;
> }
> @@ -96,12 +96,9 @@ static void setup(void)
> static void testfunc_protnone(void)
> {
> char *addr;
> - int page_sz;
>
> sig_caught = 0;
>
> - page_sz = getpagesize();
> -
> addr = SAFE_MMAP(cleanup, 0, page_sz, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
> @@ -133,7 +130,7 @@ static void testfunc_protnone(void)
>
> #ifdef __ia64__
>
> -static char exec_func[] = {
> +static char exec_func[] __attribute__ ((aligned (64))) = {
> 0x11, 0x00, 0x00, 0x00, 0x01, 0x00, /* nop.m 0x0 */
> 0x00, 0x00, 0x00, 0x02, 0x00, 0x80, /* nop.i 0x0 */
> 0x08, 0x00, 0x84, 0x00, /* br.ret.sptk.many b0;; */
> @@ -210,42 +207,33 @@ typedef struct {
> * Copy page where &exec_func resides. Also try to copy subsequent page
> * in case exec_func is close to page boundary.
> */
> -static void *get_func(void *mem)
> +static void *get_func(void *mem, uintptr_t *func_page_offset)
> {
> uintptr_t page_sz = getpagesize();
> uintptr_t page_mask = ~(page_sz - 1);
> - uintptr_t func_page_offset;
> void *func_copy_start, *page_to_copy;
> void *mem_start = mem;
>
> #ifdef USE_FUNCTION_DESCRIPTORS
> func_descr_t *opd = (func_descr_t *)&exec_func;
> - func_page_offset = (uintptr_t)opd->entry & (page_sz - 1);
> - func_copy_start = mem + func_page_offset;
> + *func_page_offset = (uintptr_t)opd->entry & (page_sz - 1);
> + func_copy_start = mem + *func_page_offset;
> page_to_copy = (void *)((uintptr_t)opd->entry & page_mask);
> #else
> - func_page_offset = (uintptr_t)&exec_func & (page_sz - 1);
> - func_copy_start = mem + func_page_offset;
> + *func_page_offset = (uintptr_t)&exec_func & (page_sz - 1);
> + func_copy_start = mem + *func_page_offset;
> page_to_copy = (void *)((uintptr_t)&exec_func & page_mask);
> #endif
> + tst_resm(TINFO, "exec_func: %p, page_to_copy: %p",
> + &exec_func, page_to_copy);
This was previously inside the body of the if statement right below.
Not sure if it was intended to always print this information, but I'm
fine either way.
>
> /* copy 1st page, if it's not present something is wrong */
> - if (!page_present(page_to_copy)) {
> - tst_resm(TINFO, "exec_func: %p, page_to_copy: %p\n",
> - &exec_func, page_to_copy);
> + if (!page_present(page_to_copy))
> tst_brkm(TBROK, cleanup, "page_to_copy not present\n");
> - }
> - memcpy(mem, page_to_copy, page_sz);
>
> - /* copy 2nd page if possible */
> - mem += page_sz;
> - page_to_copy += page_sz;
> - if (page_present(page_to_copy))
> - memcpy(mem, page_to_copy, page_sz);
> - else
> - memset(mem, 0, page_sz);
> + memcpy(mem, page_to_copy, page_sz);
>
> - clear_cache(mem_start, copy_sz);
> + clear_cache(mem_start, page_sz);
>
> /* return pointer to area where copy of exec_func resides */
> return func_copy_start;
> @@ -256,23 +244,30 @@ static void *get_func(void *mem)
> static void testfunc_protexec(void)
> {
> func_ptr_t func;
> + uintptr_t func_page_offset;
> void *p;
>
> sig_caught = 0;
>
> - p = SAFE_MMAP(cleanup, 0, copy_sz, PROT_READ | PROT_WRITE,
> + p = SAFE_MMAP(cleanup, 0, page_sz, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
> #ifdef USE_FUNCTION_DESCRIPTORS
> func_descr_t opd;
> - opd.entry = (uintptr_t)get_func(p);
> + opd.entry = (uintptr_t)get_func(p, &func_page_offset);
> func = (func_ptr_t)&opd;
> #else
> - func = get_func(p);
> + func = get_func(p, &func_page_offset);
> #endif
>
> + if (func_page_offset + 64 >= page_sz) {
I'm wondering if this should be ">" not ">=". If the compiler decides
to use the last 64 bytes in a page and locates the function at offset
0xfc0, then that's still ok: 0xfc0 + 0x40 == page_sz
> + SAFE_MUNMAP(cleanup, p, page_sz);
> + tst_brkm(TCONF, cleanup, "func too close to page boundary, "
> + "maybe your compiler ignores -falign-functions?");
> + }
> +
> /* Change the protection to PROT_EXEC. */
> - TEST(mprotect(p, copy_sz, PROT_EXEC));
> + TEST(mprotect(p, page_sz, PROT_EXEC));
>
> if (TEST_RETURN == -1) {
> tst_resm(TFAIL | TTERRNO, "mprotect failed");
> @@ -294,7 +289,7 @@ static void testfunc_protexec(void)
> }
> }
>
> - SAFE_MUNMAP(cleanup, p, copy_sz);
> + SAFE_MUNMAP(cleanup, p, page_sz);
> }
>
> static void cleanup(void)
> --
> 1.8.3.1
>
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