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Date: Tue, 16 Aug 2022 07:44:48 -0400
From: Brian Foster <bfoster@...hat.com>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: save LOC in vsyscall test
On Mon, Aug 15, 2022 at 12:50:04PM +0300, Alexey Dobriyan wrote:
> From: Brian Foster <bfoster@...hat.com>
>
> Do one fork in vsyscall detection code and let SIGSEGV handler exit and
> carry information to the parent saving LOC.
>
> [
> redo original patch,
> delete unnecessary variables,
> minimise code changes.
> --adobriyan
> ]
>
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
LGTM and passes my quick tests, thanks!
FWIW:
Reviewed-by: Brian Foster <bfoster@...hat.com>
>
> tools/testing/selftests/proc/proc-pid-vm.c | 56 ++++++++---------------------
> 1 file changed, 16 insertions(+), 40 deletions(-)
>
> --- a/tools/testing/selftests/proc/proc-pid-vm.c
> +++ b/tools/testing/selftests/proc/proc-pid-vm.c
> @@ -213,22 +213,22 @@ static int make_exe(const uint8_t *payload, size_t len)
>
> /*
> * 0: vsyscall VMA doesn't exist vsyscall=none
> - * 1: vsyscall VMA is r-xp vsyscall=emulate
> - * 2: vsyscall VMA is --xp vsyscall=xonly
> + * 1: vsyscall VMA is --xp vsyscall=xonly
> + * 2: vsyscall VMA is r-xp vsyscall=emulate
> */
> -static int g_vsyscall;
> +static volatile int g_vsyscall;
> static const char *str_vsyscall;
>
> static const char str_vsyscall_0[] = "";
> static const char str_vsyscall_1[] =
> -"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]\n";
> -static const char str_vsyscall_2[] =
> "ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]\n";
> +static const char str_vsyscall_2[] =
> +"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]\n";
>
> #ifdef __x86_64__
> static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
> {
> - _exit(1);
> + _exit(g_vsyscall);
> }
>
> /*
> @@ -255,6 +255,7 @@ static void vsyscall(void)
> act.sa_sigaction = sigaction_SIGSEGV;
> (void)sigaction(SIGSEGV, &act, NULL);
>
> + g_vsyscall = 0;
> /* gettimeofday(NULL, NULL); */
> asm volatile (
> "call %P0"
> @@ -262,45 +263,20 @@ static void vsyscall(void)
> : "i" (0xffffffffff600000), "D" (NULL), "S" (NULL)
> : "rax", "rcx", "r11"
> );
> - exit(0);
> - }
> - waitpid(pid, &wstatus, 0);
> - if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0) {
> - /* vsyscall page exists and is executable. */
> - } else {
> - /* vsyscall page doesn't exist. */
> - g_vsyscall = 0;
> - return;
> - }
> -
> - pid = fork();
> - if (pid < 0) {
> - fprintf(stderr, "fork, errno %d\n", errno);
> - exit(1);
> - }
> - if (pid == 0) {
> - struct rlimit rlim = {0, 0};
> - (void)setrlimit(RLIMIT_CORE, &rlim);
> -
> - /* Hide "segfault at ffffffffff600000" messages. */
> - struct sigaction act;
> - memset(&act, 0, sizeof(struct sigaction));
> - act.sa_flags = SA_SIGINFO;
> - act.sa_sigaction = sigaction_SIGSEGV;
> - (void)sigaction(SIGSEGV, &act, NULL);
>
> + g_vsyscall = 1;
> *(volatile int *)0xffffffffff600000UL;
> - exit(0);
> +
> + g_vsyscall = 2;
> + exit(g_vsyscall);
> }
> waitpid(pid, &wstatus, 0);
> - if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0) {
> - /* vsyscall page is readable and executable. */
> - g_vsyscall = 1;
> - return;
> + if (WIFEXITED(wstatus)) {
> + g_vsyscall = WEXITSTATUS(wstatus);
> + } else {
> + fprintf(stderr, "error: wstatus %08x\n", wstatus);
> + exit(1);
> }
> -
> - /* vsyscall page is executable but unreadable. */
> - g_vsyscall = 2;
> }
>
> int main(void)
>
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