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guard: works on macOS

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This commit is contained in:
Matthew LeVan 2024-02-19 12:54:43 -05:00
parent 45f47e069f
commit b1960ad1f6
1 changed files with 20 additions and 44 deletions
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64
rust/ares_guard/c-src/guard.c
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@ -31,7 +31,7 @@ _prot_page(void *address, int prot)
return guard_mprotect | errno;
}
return 0;
return guard_success;
}
static guard_result
@ -47,8 +47,6 @@ _unmark_page(void *address)
}
// Center the guard page.
// XX: could be a false positive if the new frame results in exact same guard page
// solution: we only re-center from the signal handler
static guard_result
_focus_guard()
{
@ -58,39 +56,30 @@ _focus_guard()
uintptr_t new_guard_p;
guard_result err = 0;
// fprintf(stderr, "guard: focus: stack pointer at %p\r\n", (void *)stack_p);
// fprintf(stderr, "guard: focus: alloc pointer at %p\r\n", (void *)alloc_p);
if (stack_p == 0 || alloc_p == 0) {
fprintf(stderr, "guard: focus: stack or alloc pointer is null\r\n");
return guard_null;
} else if (stack_p == alloc_p) {
// fprintf(stderr, "guard: focus: stack and alloc pointers equal\r\n");
fprintf(stderr, "guard: focus: stack and alloc pointers equal\r\n");
return guard_oom;
}
// fprintf(stderr, "guard: focus: old guard = %p\r\n", (void *)old_guard_p);
// Compute new guard page
// XX: Should we also check for new_guard_p < min(stack_p, alloc_p)?
// Compute new guard page.
new_guard_p = GD_PAGE_ROUND_DOWN((stack_p + alloc_p) / 2);
// fprintf(stderr, "guard: focus: new guard = %p\r\n", (void *)new_guard_p);
if (new_guard_p == old_guard_p) {
// fprintf(stderr, "guard: focus: OOM\r\n");
return guard_oom;
}
// Mark new guard page
// Mark new guard page.
if ((err = _mark_page((void *)new_guard_p))) {
fprintf(stderr, "guard: focus: mark error\r\n");
return err;
}
// Update guard page tracker
// fprintf(stderr, "guard: focus: installed guard at %p\r\n", (void *)new_guard_p);
// Update guard page tracker.
guard_p = new_guard_p;
// Unmark the old guard page (if there is one)
// Unmark the old guard page if there is one.
if (old_guard_p) {
if ((err = _unmark_page((void *)old_guard_p))) {
fprintf(stderr, "guard: focus: unmark error\r\n");
@ -98,7 +87,7 @@ _focus_guard()
}
}
return 0;
return guard_success;
}
static void
@ -109,28 +98,22 @@ _signal_handler(int sig, siginfo_t *si, void *unused)
assert(guard_p);
// fprintf(stderr, "guard: handler: %d received\r\n", sig);
if (sig != SIGSEGV && sig != SIGBUS) {
fprintf(stderr, "guard: handler: invalid signal: %d\r\n", sig);
assert(0);
}
sig_addr = (uintptr_t)si->si_addr;
// fprintf(stderr, "guard: SIGSEGV address = %p\r\n", (void *)sig_addr);
if (sig_addr >= guard_p &&
sig_addr < guard_p + GD_PAGE_SIZE)
{
// fprintf(stderr, "guard: hit: %p\r\n", si->si_addr);
err = _focus_guard();
if (err) {
// fprintf(stderr, "guard: handler: focus error\r\n");
siglongjmp(buffer_list->buffer, err);
}
}
else {
// fprintf(stderr, "guard: page at %p miss\r\n", (void *)guard_p);
switch (sig) {
case SIGSEGV: {
if (prev_sigsegv_sa.sa_sigaction != NULL) {
@ -155,14 +138,14 @@ _signal_handler(int sig, siginfo_t *si, void *unused)
}
}
// Registers the same handler function for SIGSEGV and SIGBUS.
static guard_result
_register_handler()
_register_handlers()
{
struct sigaction sa;
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = _signal_handler;
// XX should assert that prev_sigsegv_sa is uninitialized, but it's non-trivial
if (sigaction(SIGSEGV, &sa, &prev_sigsegv_sa)) {
fprintf(stderr, "guard: register: sigaction error\r\n");
fprintf(stderr, "%s\r\n", strerror(errno));
@ -175,7 +158,7 @@ _register_handler()
return guard_sigaction | errno;
}
return 0;
return guard_success;
}
guard_result
@ -184,29 +167,26 @@ guard(
void *closure,
const uintptr_t *const s_pp,
const uintptr_t *const a_pp,
void ** ret
void **ret
) {
GD_buflistnode *new_buffer;
guard_result err = 0;
guard_result td_err = 0;
// fprintf(stderr, "guard: stack pointer at %p\r\n", (void *)(*s_pp));
// fprintf(stderr, "guard: alloc pointer at %p\r\n", (void *)(*a_pp));
if (guard_p == 0) {
assert(buffer_list == NULL);
stack_pp = s_pp;
alloc_pp = a_pp;
// Initialize the guard page
// Initialize the guard page.
if ((err = _focus_guard())) {
fprintf(stderr, "guard: initial focus error\r\n");
goto exit;
}
// Register guard page signal handler
if ((err = _register_handler())) {
// Register guard page signal handler.
if ((err = _register_handlers())) {
fprintf(stderr, "guard: registration error\r\n");
goto clean;
}
@ -214,7 +194,7 @@ guard(
assert(buffer_list != NULL);
}
// Setup new longjmp buffer
// Setup new longjmp buffer.
new_buffer = (GD_buflistnode *)malloc(sizeof(GD_buflistnode));
if (new_buffer == NULL) {
fprintf(stderr, "guard: malloc error\r\n");
@ -225,22 +205,19 @@ guard(
new_buffer->next = buffer_list;
buffer_list = new_buffer;
// Run given closure
// fprintf(stderr, "guard: run\r\n");
// Run given closure.
if (!(err = sigsetjmp(buffer_list->buffer, 1))) {
*ret = f(closure);
}
// Restore previous longjmp buffer
// Restore previous longjmp buffer.
buffer_list = buffer_list->next;
free((void *)new_buffer);
skip:
// If no more guarded closures, then...
if (buffer_list == NULL) {
// Remove new signal handlers
if (sigaction(SIGSEGV, &prev_sigsegv_sa, NULL)) {
fprintf(stderr, "guard: sigaction error\r\n");
fprintf(stderr, "guard: error replacing sigsegv handler\r\n");
fprintf(stderr, "%s\r\n", strerror(errno));
td_err = guard_sigaction | errno;
@ -249,7 +226,7 @@ skip:
}
}
if (sigaction(SIGBUS, &prev_sigbus_sa, NULL)) {
fprintf(stderr, "guard: sigaction error\r\n");
fprintf(stderr, "guard: error replacing sigbus handler\r\n");
fprintf(stderr, "%s\r\n", strerror(errno));
td_err = guard_sigaction | errno;
@ -259,7 +236,7 @@ skip:
}
clean:
// Unmark guard page
// Unmark guard page.
assert(guard_p != 0);
td_err = _unmark_page((void *)guard_p);
if (td_err) {
@ -273,6 +250,5 @@ clean:
}
exit:
// fprintf(stderr, "guard: return\r\n");
return err;
}