diff options
Diffstat (limited to 'nptl')
| -rw-r--r-- | nptl/allocatestack.c | 66 |
1 files changed, 58 insertions, 8 deletions
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c index e5c5f79..8364406 100644 --- a/nptl/allocatestack.c +++ b/nptl/allocatestack.c @@ -334,6 +334,43 @@ change_stack_perm (struct pthread *pd return 0; } +/* Return the guard page position on allocated stack. */ +static inline char * +__attribute ((always_inline)) +guard_position (void *mem, size_t size, size_t guardsize, struct pthread *pd, + size_t pagesize_m1) +{ +#ifdef NEED_SEPARATE_REGISTER_STACK + return mem + (((size - guardsize) / 2) & ~pagesize_m1); +#elif _STACK_GROWS_DOWN + return mem; +#elif _STACK_GROWS_UP + return (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1); +#endif +} + +/* Based on stack allocated with PROT_NONE, setup the required portions with + 'prot' flags based on the guard page position. */ +static inline int +setup_stack_prot (char *mem, size_t size, char *guard, size_t guardsize, + const int prot) +{ + char *guardend = guard + guardsize; +#if _STACK_GROWS_DOWN + /* As defined at guard_position, for architectures with downward stack + the guard page is always at start of the allocated area. */ + if (mprotect (guardend, size - guardsize, prot) != 0) + return errno; +#else + size_t mprots1 = (uintptr_t) guard - (uintptr_t) mem; + if (mprotect (mem, mprots1, prot) != 0) + return errno; + size_t mprots2 = ((uintptr_t) mem + size) - (uintptr_t) guardend; + if (mprotect (guardend, mprots2, prot) != 0) + return errno; +#endif + return 0; +} /* Returns a usable stack for a new thread either by allocating a new stack or reusing a cached stack of sufficient size. @@ -490,7 +527,10 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp, size += pagesize_m1 + 1; #endif - mem = mmap (NULL, size, prot, + /* If a guard page is required, avoid committing memory by first + allocate with PROT_NONE and then reserve with required permission + excluding the guard page. */ + mem = mmap (NULL, size, (guardsize == 0) ? prot : PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0); if (__glibc_unlikely (mem == MAP_FAILED)) @@ -510,9 +550,24 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp, - TLS_PRE_TCB_SIZE); #endif + /* Now mprotect the required region excluding the guard area. */ + if (__glibc_likely (guardsize > 0)) + { + char *guard = guard_position (mem, size, guardsize, pd, + pagesize_m1); + if (setup_stack_prot (mem, size, guard, guardsize, prot) != 0) + { + munmap (mem, size); + return errno; + } + } + /* Remember the stack-related values. */ pd->stackblock = mem; pd->stackblock_size = size; + /* Update guardsize for newly allocated guardsize to avoid + an mprotect in guard resize below. */ + pd->guardsize = guardsize; /* We allocated the first block thread-specific data array. This address will not change for the lifetime of this @@ -593,13 +648,8 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp, /* Create or resize the guard area if necessary. */ if (__glibc_unlikely (guardsize > pd->guardsize)) { -#ifdef NEED_SEPARATE_REGISTER_STACK - char *guard = mem + (((size - guardsize) / 2) & ~pagesize_m1); -#elif _STACK_GROWS_DOWN - char *guard = mem; -#elif _STACK_GROWS_UP - char *guard = (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1); -#endif + char *guard = guard_position (mem, size, guardsize, pd, + pagesize_m1); if (mprotect (guard, guardsize, PROT_NONE) != 0) { mprot_error: |