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add guard pages to the internal signal stacks

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Signal handlers tend to be lean, but can still overflow the (tiny)
stack.

Change-Id: Ia21c6453d92a9f8d1536ad01ff26a1a84c05f8fb
This commit is contained in:
Daniel Micay 2015-03-29 00:03:55 -04:00
parent 203082b821
commit 595752f623
3 changed files with 16 additions and 7 deletions
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18
libc/bionic/pthread_create.cpp
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@ -69,17 +69,23 @@ void __init_tls(pthread_internal_t* thread) {
void __init_alternate_signal_stack(pthread_internal_t* thread) { void __init_alternate_signal_stack(pthread_internal_t* thread) {
// Create and set an alternate signal stack. // Create and set an alternate signal stack.
stack_t ss; void* stack_base = mmap(NULL, SIGNAL_STACK_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
ss.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); if (stack_base != MAP_FAILED) {
if (ss.ss_sp != MAP_FAILED) { // Create a guard page to catch stack overflows in signal handlers.
ss.ss_size = SIGSTKSZ; if (mprotect(stack_base, PAGE_SIZE, PROT_NONE) == -1) {
munmap(stack_base, SIGNAL_STACK_SIZE);
return;
}
stack_t ss;
ss.ss_sp = stack_base + PAGE_SIZE;
ss.ss_size = SIGNAL_STACK_SIZE - PAGE_SIZE;
ss.ss_flags = 0; ss.ss_flags = 0;
sigaltstack(&ss, NULL); sigaltstack(&ss, NULL);
thread->alternate_signal_stack = ss.ss_sp; thread->alternate_signal_stack = stack_base;
// We can only use const static allocated string for mapped region name, as Android kernel // We can only use const static allocated string for mapped region name, as Android kernel
// uses the string pointer directly when dumping /proc/pid/maps. // uses the string pointer directly when dumping /proc/pid/maps.
prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack"); prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, stack_base, SIGNAL_STACK_SIZE, "thread signal stack");
} }
} }

2
libc/bionic/pthread_exit.cpp
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@ -87,7 +87,7 @@ void pthread_exit(void* return_value) {
sigaltstack(&ss, NULL); sigaltstack(&ss, NULL);
// Free it. // Free it.
munmap(thread->alternate_signal_stack, SIGSTKSZ); munmap(thread->alternate_signal_stack, SIGNAL_STACK_SIZE);
thread->alternate_signal_stack = NULL; thread->alternate_signal_stack = NULL;
} }

3
libc/bionic/pthread_internal.h
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@ -130,6 +130,9 @@ __LIBC_HIDDEN__ void pthread_key_clean_all(void);
*/ */
#define PTHREAD_STACK_SIZE_DEFAULT ((1 * 1024 * 1024) - SIGSTKSZ) #define PTHREAD_STACK_SIZE_DEFAULT ((1 * 1024 * 1024) - SIGSTKSZ)
/* Leave room for a guard page in the internally created signal stacks. */
#define SIGNAL_STACK_SIZE (SIGSTKSZ + PAGE_SIZE)
/* Needed by fork. */ /* Needed by fork. */
__LIBC_HIDDEN__ extern void __bionic_atfork_run_prepare(); __LIBC_HIDDEN__ extern void __bionic_atfork_run_prepare();
__LIBC_HIDDEN__ extern void __bionic_atfork_run_child(); __LIBC_HIDDEN__ extern void __bionic_atfork_run_child();