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Date: Thu, 27 Jun 2019 10:29:01 -0700
From: Kees Cook <keescook@...omium.org>
To: Andy Lutomirski <luto@...nel.org>
Cc: x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
Florian Weimer <fweimer@...hat.com>, Jann Horn <jannh@...gle.com>,
Borislav Petkov <bp@...en8.de>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 5/8] selftests/x86/vsyscall: Verify that vsyscall=none
blocks execution
On Wed, Jun 26, 2019 at 09:45:06PM -0700, Andy Lutomirski wrote:
> If vsyscall=none accidentally still allowed vsyscalls, the test
> wouldn't fail. Fix it.
>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> tools/testing/selftests/x86/test_vsyscall.c | 76 ++++++++++++++-------
> 1 file changed, 52 insertions(+), 24 deletions(-)
>
> diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
> index 4c9a8d76dba0..34a1d35995ef 100644
> --- a/tools/testing/selftests/x86/test_vsyscall.c
> +++ b/tools/testing/selftests/x86/test_vsyscall.c
> @@ -49,21 +49,21 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
> }
>
> /* vsyscalls and vDSO */
> -bool should_read_vsyscall = false;
> +bool vsyscall_map_r = false, vsyscall_map_x = false;
>
> typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
> -gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
> +const gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
> gtod_t vdso_gtod;
>
> typedef int (*vgettime_t)(clockid_t, struct timespec *);
> vgettime_t vdso_gettime;
>
> typedef long (*time_func_t)(time_t *t);
> -time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
> +const time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
> time_func_t vdso_time;
>
> typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
> -getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
> +const getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
> getcpu_t vdso_getcpu;
>
> static void init_vdso(void)
> @@ -107,7 +107,7 @@ static int init_vsys(void)
> maps = fopen("/proc/self/maps", "r");
> if (!maps) {
> printf("[WARN]\tCould not open /proc/self/maps -- assuming vsyscall is r-x\n");
> - should_read_vsyscall = true;
> + vsyscall_map_r = true;
> return 0;
> }
>
> @@ -133,12 +133,8 @@ static int init_vsys(void)
> }
>
> printf("\tvsyscall permissions are %c-%c\n", r, x);
> - should_read_vsyscall = (r == 'r');
> - if (x != 'x') {
> - vgtod = NULL;
> - vtime = NULL;
> - vgetcpu = NULL;
> - }
> + vsyscall_map_r = (r == 'r');
> + vsyscall_map_x = (x == 'x');
>
> found = true;
> break;
> @@ -148,10 +144,8 @@ static int init_vsys(void)
>
> if (!found) {
> printf("\tno vsyscall map in /proc/self/maps\n");
> - should_read_vsyscall = false;
> - vgtod = NULL;
> - vtime = NULL;
> - vgetcpu = NULL;
> + vsyscall_map_r = false;
> + vsyscall_map_x = false;
> }
>
> return nerrs;
> @@ -242,7 +236,7 @@ static int test_gtod(void)
> err(1, "syscall gettimeofday");
> if (vdso_gtod)
> ret_vdso = vdso_gtod(&tv_vdso, &tz_vdso);
> - if (vgtod)
> + if (vsyscall_map_x)
> ret_vsys = vgtod(&tv_vsys, &tz_vsys);
> if (sys_gtod(&tv_sys2, &tz_sys) != 0)
> err(1, "syscall gettimeofday");
> @@ -256,7 +250,7 @@ static int test_gtod(void)
> }
> }
>
> - if (vgtod) {
> + if (vsyscall_map_x) {
> if (ret_vsys == 0) {
> nerrs += check_gtod(&tv_sys1, &tv_sys2, &tz_sys, "vsyscall", &tv_vsys, &tz_vsys);
> } else {
> @@ -277,7 +271,7 @@ static int test_time(void) {
> t_sys1 = sys_time(&t2_sys1);
> if (vdso_time)
> t_vdso = vdso_time(&t2_vdso);
> - if (vtime)
> + if (vsyscall_map_x)
> t_vsys = vtime(&t2_vsys);
> t_sys2 = sys_time(&t2_sys2);
> if (t_sys1 < 0 || t_sys1 != t2_sys1 || t_sys2 < 0 || t_sys2 != t2_sys2) {
> @@ -298,7 +292,7 @@ static int test_time(void) {
> }
> }
>
> - if (vtime) {
> + if (vsyscall_map_x) {
> if (t_vsys < 0 || t_vsys != t2_vsys) {
> printf("[FAIL]\tvsyscall failed (ret:%ld output:%ld)\n", t_vsys, t2_vsys);
> nerrs++;
> @@ -334,7 +328,7 @@ static int test_getcpu(int cpu)
> ret_sys = sys_getcpu(&cpu_sys, &node_sys, 0);
> if (vdso_getcpu)
> ret_vdso = vdso_getcpu(&cpu_vdso, &node_vdso, 0);
> - if (vgetcpu)
> + if (vsyscall_map_x)
> ret_vsys = vgetcpu(&cpu_vsys, &node_vsys, 0);
>
> if (ret_sys == 0) {
> @@ -373,7 +367,7 @@ static int test_getcpu(int cpu)
> }
> }
>
> - if (vgetcpu) {
> + if (vsyscall_map_x) {
> if (ret_vsys) {
> printf("[FAIL]\tvsyscall getcpu() failed\n");
> nerrs++;
> @@ -414,10 +408,10 @@ static int test_vsys_r(void)
> can_read = false;
> }
>
> - if (can_read && !should_read_vsyscall) {
> + if (can_read && !vsyscall_map_r) {
> printf("[FAIL]\tWe have read access, but we shouldn't\n");
> return 1;
> - } else if (!can_read && should_read_vsyscall) {
> + } else if (!can_read && vsyscall_map_r) {
> printf("[FAIL]\tWe don't have read access, but we should\n");
> return 1;
> } else if (can_read) {
> @@ -431,6 +425,39 @@ static int test_vsys_r(void)
> return 0;
> }
>
> +static int test_vsys_x(void)
> +{
> +#ifdef __x86_64__
> + if (vsyscall_map_x) {
> + /* We already tested this adequately. */
> + return 0;
> + }
> +
> + printf("[RUN]\tMake sure that vsyscalls really page fault\n");
> +
> + bool can_exec;
> + if (sigsetjmp(jmpbuf, 1) == 0) {
> + vgtod(NULL, NULL);
> + can_exec = true;
> + } else {
> + can_exec = false;
> + }
> +
> + if (can_exec) {
> + printf("[FAIL]\tExecuting the vsyscall did not page fault\n");
> + return 1;
> + } else if (segv_err & (1 << 4)) { /* INSTR */
> + printf("[OK]\tExecuting the vsyscall page failed: #PF(0x%lx)\n",
> + segv_err);
> + } else {
> + printf("[FAILT]\tExecution failed with the wrong error: #PF(0x%lx)\n",
> + segv_err);
> + return 1;
> + }
> +#endif
> +
> + return 0;
> +}
>
> #ifdef __x86_64__
> #define X86_EFLAGS_TF (1UL << 8)
> @@ -462,7 +489,7 @@ static int test_emulation(void)
> time_t tmp;
> bool is_native;
>
> - if (!vtime)
> + if (!vsyscall_map_x)
> return 0;
>
> printf("[RUN]\tchecking that vsyscalls are emulated\n");
> @@ -504,6 +531,7 @@ int main(int argc, char **argv)
>
> sethandler(SIGSEGV, sigsegv, 0);
> nerrs += test_vsys_r();
> + nerrs += test_vsys_x();
>
> #ifdef __x86_64__
> nerrs += test_emulation();
> --
> 2.21.0
>
--
Kees Cook
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