| From: Kees Cook <kees@kernel.org> |
| Subject: mm: vmalloc: only zero-init on vrealloc shrink |
| Date: Thu, 15 May 2025 14:42:16 -0700 |
| |
| The common case is to grow reallocations, and since init_on_alloc will |
| have already zeroed the whole allocation, we only need to zero when |
| shrinking the allocation. |
| |
| Link: https://lkml.kernel.org/r/20250515214217.619685-2-kees@kernel.org |
| Fixes: a0309faf1cb0 ("mm: vmalloc: support more granular vrealloc() sizing") |
| Signed-off-by: Kees Cook <kees@kernel.org> |
| Tested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> |
| Cc: Danilo Krummrich <dakr@kernel.org> |
| Cc: Eduard Zingerman <eddyz87@gmail.com> |
| Cc: "Erhard F." <erhard_f@mailbox.org> |
| Cc: Shung-Hsi Yu <shung-hsi.yu@suse.com> |
| Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com> |
| Cc: <stable@vger.kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| mm/vmalloc.c | 12 +++++++----- |
| 1 file changed, 7 insertions(+), 5 deletions(-) |
| |
| --- a/mm/vmalloc.c~mm-vmalloc-only-zero-init-on-vrealloc-shrink |
| +++ a/mm/vmalloc.c |
| @@ -4093,8 +4093,8 @@ void *vrealloc_noprof(const void *p, siz |
| * would be a good heuristic for when to shrink the vm_area? |
| */ |
| if (size <= old_size) { |
| - /* Zero out "freed" memory. */ |
| - if (want_init_on_free()) |
| + /* Zero out "freed" memory, potentially for future realloc. */ |
| + if (want_init_on_free() || want_init_on_alloc(flags)) |
| memset((void *)p + size, 0, old_size - size); |
| vm->requested_size = size; |
| kasan_poison_vmalloc(p + size, old_size - size); |
| @@ -4107,9 +4107,11 @@ void *vrealloc_noprof(const void *p, siz |
| if (size <= alloced_size) { |
| kasan_unpoison_vmalloc(p + old_size, size - old_size, |
| KASAN_VMALLOC_PROT_NORMAL); |
| - /* Zero out "alloced" memory. */ |
| - if (want_init_on_alloc(flags)) |
| - memset((void *)p + old_size, 0, size - old_size); |
| + /* |
| + * No need to zero memory here, as unused memory will have |
| + * already been zeroed at initial allocation time or during |
| + * realloc shrink time. |
| + */ |
| vm->requested_size = size; |
| return (void *)p; |
| } |
| _ |
