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Don't expose guard pages to malloc_stack API consumers #54591

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merged 1 commit into from
Jun 9, 2024
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Don't expose guard pages to malloc_stack API consumers #54591

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30 changes: 29 additions & 1 deletion src/gc-stacks.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,13 +22,22 @@
// 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 @@ -39,6 +48,7 @@ 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 @@ -47,6 +57,12 @@ static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT

static void free_stack(void *stkbuf, size_t bufsz)
{
#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);
}
Expand All @@ -72,16 +88,22 @@ static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT
# 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;

#if !defined(JL_HAVE_UCONTEXT) && !defined(JL_HAVE_SIGALTSTACK)
#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

jl_atomic_fetch_add_relaxed(&num_stack_mappings, 1);
Expand All @@ -91,6 +113,12 @@ static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT

static void free_stack(void *stkbuf, size_t bufsz)
{
#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);
}
Expand Down