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Harden core engine against integer overflows, allocator canary recovery, and SSA shift range unsoundness #24590

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b29fd22
Harden core engine against integer overflows, canary leaks, and range…
mkrishna793 Oct 23, 2026
8997a80
Merge branch 'php:master' into master
mkrishna793 Oct 23, 2026
33f6ad0
Address review feedback: remove proofs, revert external libs, make ch…
mkrishna793 Oct 28, 2026
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12 changes: 7 additions & 5 deletions Zend/Optimizer/zend_inference.c
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Original file line number Diff line number Diff line change
Expand Up @@ -760,12 +760,14 @@ static inline zend_long safe_shift_left(zend_long n, zend_long s) {
}

static inline bool shift_left_overflows(zend_long n, zend_long s) {
/* This considers shifts that shift in the sign bit to be overflowing as well */
if (n >= 0) {
return s >= SIZEOF_ZEND_LONG * 8 - 1 || safe_shift_left(n, s) < n;
} else {
return s >= SIZEOF_ZEND_LONG * 8 || safe_shift_left(n, s) > n;
if (UNEXPECTED((zend_ulong)s >= SIZEOF_ZEND_LONG * 8)) {
return true;
}
if (UNEXPECTED(s == SIZEOF_ZEND_LONG * 8 - 1)) {
return n != 0 && n != -1;
}
zend_long shifted = (zend_long)((zend_ulong)n << (zend_ulong)s);
return (shifted >> s) != n;
}

@arnaud-lb arnaud-lb Oct 23, 2026

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Please submit this as a separate PR on the PHP-8.4 branch with a test:

--TEST--
Too narrow range inferred for SL when the shift wraps
--SKIPIF--
<?php if (PHP_INT_SIZE != 8) die("skip 64-bit only"); ?>
--FILE--
<?php
/* $i is inferred as RANGE[1..5]. Shifting it by 62 wraps for every $i >= 2,
 * so the result range may not be derived from the two endpoints: both of them
 * happen to yield 1 << 62, while the values in between do not. */
function shift_positive(): array {
    $out = [];
    for ($i = 1; $i <= 5; $i++) {
        $out[] = $i << 62;
    }
    return $out;
}

/* Likewise for RANGE[-3..-1] shifted by 63: both endpoints yield LONG_MIN,
 * but -2 << 63 is 0. */
function shift_negative(): array {
    $out = [];
    for ($i = -1; $i >= -3; $i--) {
        $out[] = $i << 63;
    }
    return $out;
}

var_dump(shift_positive());
var_dump(shift_negative());
?>
--EXPECT--
array(5) {
  [0]=>
  int(4611686018427387904)
  [1]=>
  int(-9223372036854775808)
  [2]=>
  int(-4611686018427387904)
  [3]=>
  int(0)
  [4]=>
  int(4611686018427387904)
}
array(3) {
  [0]=>
  int(-9223372036854775808)
  [1]=>
  int(0)
  [2]=>
  int(-9223372036854775808)
}


/* If b does not divide a exactly, return the two adjacent values between which the real result
Expand Down
14 changes: 8 additions & 6 deletions Zend/zend_alloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1034,19 +1034,21 @@ static zend_always_inline void zend_mm_chunk_init(zend_mm_heap *heap, zend_mm_ch
static zend_always_inline zend_mm_chunk *zend_mm_encode_cached_chunk(const zend_mm_heap *heap, const void *holder, const zend_mm_chunk *next)
{
#ifdef WORDS_BIGENDIAN
return (zend_mm_chunk*)((uintptr_t)next ^ heap->shadow_key ^ (uintptr_t)holder);
uintptr_t p = (uintptr_t)next;
#else
return (zend_mm_chunk*)(BSWAPPTR((uintptr_t)next) ^ heap->shadow_key ^ (uintptr_t)holder);
uintptr_t p = BSWAPPTR((uintptr_t)next);
#endif
/* ARX (Addition-XOR) non-linear mixing prevents linear algebraic shadow_key recovery */
return (zend_mm_chunk*)((p + heap->shadow_key) ^ (uintptr_t)holder);
Comment on lines +1041 to +1042

@arnaud-lb arnaud-lb Oct 23, 2026

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Could you explain this change?

}

static zend_always_inline zend_mm_chunk *zend_mm_decode_cached_chunk_key(uintptr_t key, const void *holder, const zend_mm_chunk *encoded)
{
#ifdef WORDS_BIGENDIAN
zend_mm_chunk *next = (zend_mm_chunk*)((uintptr_t)encoded ^ key ^ (uintptr_t)holder);
#else
zend_mm_chunk *next = (zend_mm_chunk*)(BSWAPPTR((uintptr_t)encoded ^ key ^ (uintptr_t)holder));
uintptr_t p = ((uintptr_t)encoded ^ (uintptr_t)holder) - key;
#ifndef WORDS_BIGENDIAN
p = BSWAPPTR(p);
#endif
zend_mm_chunk *next = (zend_mm_chunk*)p;

ZEND_MM_CHECK(ZEND_MM_ALIGNED_OFFSET(next, ZEND_MM_CHUNK_SIZE) == 0, "zend_mm_heap corrupted");
return next;
Expand Down
5 changes: 4 additions & 1 deletion Zend/zend_gc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -421,7 +421,10 @@ static zend_always_inline gc_root_buffer* gc_decompress(zend_refcounted *ref, ui

while (1) {
idx += GC_MAX_UNCOMPRESSED;
ZEND_ASSERT(idx < GC_G(first_unused));
if (UNEXPECTED(idx >= GC_G(first_unused))) {
zend_error_noreturn(E_CORE_ERROR, "GC root buffer corruption detected: unable to resolve compressed address");
return NULL;
}
Comment on lines +424 to +427

@arnaud-lb arnaud-lb Oct 23, 2026

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Could you explain when this happens?

root = GC_IDX2PTR(idx);
if (GC_GET_PTR(root->ref) == ref) {
return root;
Expand Down
24 changes: 18 additions & 6 deletions main/streams/memory.c
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Expand Up @@ -52,8 +52,12 @@ static ssize_t php_stream_memory_write(php_stream *stream, const char *buf, size
if (ms->mode & TEMP_STREAM_APPEND) {
ms->fpos = data_len;
}
if (ms->fpos + count > data_len) {
zend_string *grown = zend_string_frealloc(ms->data, ms->fpos + count, 0, /* fallible */ true);
if (UNEXPECTED(count > SIZE_MAX - ms->fpos)) {
return (ssize_t) -1;
}
size_t new_pos = ms->fpos + count;
if (new_pos > data_len) {
zend_string *grown = zend_string_frealloc(ms->data, new_pos, 0, /* fallible */ true);
if (UNEXPECTED(!grown)) {
return (ssize_t) -1;
}
Expand All @@ -69,7 +73,7 @@ static ssize_t php_stream_memory_write(php_stream *stream, const char *buf, size
ZEND_ASSERT(buf != NULL);
memcpy(ZSTR_VAL(ms->data) + ms->fpos, (char*) buf, count);
ZSTR_VAL(ms->data)[ZSTR_LEN(ms->data)] = '\0';
ms->fpos += count;
ms->fpos = new_pos;
}
return count;
}
Expand Down Expand Up @@ -142,9 +146,13 @@ static int php_stream_memory_seek(php_stream *stream, zend_off_t offset, int whe
return 0;
}
} else {
if (UNEXPECTED((size_t)offset > SIZE_MAX - ms->fpos)) {
*newoffs = -1;
return -1;
}
stream->eof = 0;
stream->fatal_error = 0;
ms->fpos = ms->fpos + offset;
ms->fpos += (size_t)offset;
*newoffs = ms->fpos;
return 0;
}
Expand All @@ -154,15 +162,19 @@ static int php_stream_memory_seek(php_stream *stream, zend_off_t offset, int whe
*newoffs = -1;
return -1;
} else {
ms->fpos = offset;
ms->fpos = (size_t)offset;
*newoffs = ms->fpos;
stream->eof = 0;
stream->fatal_error = 0;
return 0;
}
case SEEK_END:
if (offset > 0) {
ms->fpos = ZSTR_LEN(ms->data) + offset;
if (UNEXPECTED((size_t)offset > SIZE_MAX - ZSTR_LEN(ms->data))) {
*newoffs = -1;
return -1;
}
ms->fpos = ZSTR_LEN(ms->data) + (size_t)offset;
*newoffs = ms->fpos;
stream->eof = 0;
stream->fatal_error = 0;
Expand Down
3 changes: 3 additions & 0 deletions main/streams/userspace.c
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Expand Up @@ -612,6 +612,9 @@ static ssize_t php_userstreamop_write(php_stream *stream, const char *buf, size_
} else {
convert_to_long(&retval);
didwrite = Z_LVAL(retval);
if (didwrite < 0) {
didwrite = -1;
Comment on lines +615 to +616

@arnaud-lb arnaud-lb Oct 23, 2026

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Please submit this as a separate PR on the PHP-8.4 branch with a test

}
}

/* don't allow strange buffer overruns due to bogus return */
Expand Down
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