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Revert "Don't expose guard pages to malloc_stack API consumers" (#55555)
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Reverts #54591

This cause the runtime to misbehave and crash, since all of the
consumers of this information in the runtime assumed that the guard
pages are accounted for correctly as part of the reserved allocation.
Nothing in the runtime ever promised that it is valid to access the
pages beyond the current redzone (indeed, ASAN would forbid it as well).
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vtjnash authored and KristofferC committed Sep 12, 2024
1 parent 96f9b6b commit 399512f
Showing 1 changed file with 5 additions and 42 deletions.
47 changes: 5 additions & 42 deletions src/gc-stacks.c
Original file line number Diff line number Diff line change
Expand Up @@ -23,22 +23,13 @@
// number of stacks to always keep available per pool
#define MIN_STACK_MAPPINGS_PER_POOL 5

#if defined(_OS_WINDOWS_) || (!defined(_OS_OPENBSD_) && !defined(JL_HAVE_UCONTEXT) && !defined(JL_HAVE_SIGALTSTACK))
#define JL_USE_GUARD_PAGE 1
const size_t jl_guard_size = (4096 * 8);
#else
const size_t jl_guard_size = 0;
#endif

static _Atomic(uint32_t) num_stack_mappings = 0;

#ifdef _OS_WINDOWS_
#define MAP_FAILED NULL
static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT
{
size_t guard_size = LLT_ALIGN(jl_guard_size, jl_page_size);
bufsz += guard_size;

void *stk = VirtualAlloc(NULL, bufsz, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
if (stk == NULL)
return MAP_FAILED;
Expand All @@ -49,7 +40,6 @@ static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT
VirtualFree(stk, 0, MEM_RELEASE);
return MAP_FAILED;
}
stk = (char *)stk + guard_size;

jl_atomic_fetch_add_relaxed(&num_stack_mappings, 1);
return stk;
Expand All @@ -58,68 +48,41 @@ static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT

static void free_stack(void *stkbuf, size_t bufsz) JL_NOTSAFEPOINT
{
#ifdef JL_USE_GUARD_PAGE
size_t guard_size = LLT_ALIGN(jl_guard_size, jl_page_size);
bufsz += guard_size;
stkbuf = (char *)stkbuf - guard_size;
#endif

VirtualFree(stkbuf, 0, MEM_RELEASE);
jl_atomic_fetch_add_relaxed(&num_stack_mappings, -1);
}

#else

# ifdef _OS_OPENBSD_
static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT
{
void* stk = mmap(0, bufsz, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
if (stk == MAP_FAILED)
return MAP_FAILED;

# ifdef _OS_OPENBSD_
// we don't set up a guard page to detect stack overflow: on OpenBSD, any
// mmap-ed region has guard page managed by the kernel, so there is no
// need for it. Additionally, a memory region used as stack (memory
// allocated with MAP_STACK option) has strict permission, and you can't
// "create" a guard page on such memory by using `mprotect` on it

jl_atomic_fetch_add_relaxed(&num_stack_mappings, 1);
return stk;
}
void* stk = mmap(0, bufsz, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
if (stk == MAP_FAILED)
return MAP_FAILED;
# else
static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT
{
#ifdef JL_USE_GUARD_PAGE
size_t guard_size = LLT_ALIGN(jl_guard_size, jl_page_size);
bufsz += guard_size;
#endif

void* stk = mmap(0, bufsz, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (stk == MAP_FAILED)
return MAP_FAILED;

#ifdef JL_USE_GUARD_PAGE
// set up a guard page to detect stack overflow
if (mprotect(stk, jl_guard_size, PROT_NONE) == -1) {
munmap(stk, bufsz);
return MAP_FAILED;
}
stk = (char *)stk + guard_size;
#endif
# endif

jl_atomic_fetch_add_relaxed(&num_stack_mappings, 1);
return stk;
}
# endif

static void free_stack(void *stkbuf, size_t bufsz) JL_NOTSAFEPOINT
{
#ifdef JL_USE_GUARD_PAGE
size_t guard_size = LLT_ALIGN(jl_guard_size, jl_page_size);
bufsz += guard_size;
stkbuf = (char *)stkbuf - guard_size;
#endif

munmap(stkbuf, bufsz);
jl_atomic_fetch_add_relaxed(&num_stack_mappings, -1);
}
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