Merge tag 'slab-for-6.11' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab

Pull slab updates from Vlastimil Babka:
 "The most prominent change this time is the kmem_buckets based
  hardening of kmalloc() allocations from Kees Cook.

  We have also extended the kmalloc() alignment guarantees for
  non-power-of-two sizes in a way that benefits rust.

  The rest are various cleanups and non-critical fixups.

   - Dedicated bucket allocator (Kees Cook)

     This series [1] enhances the probabilistic defense against heap
     spraying/grooming of CONFIG_RANDOM_KMALLOC_CACHES from last year.

     kmalloc() users that are known to be useful for exploits can get
     completely separate set of kmalloc caches that can't be shared with
     other users. The first converted users are alloc_msg() and
     memdup_user().

     The hardening is enabled by CONFIG_SLAB_BUCKETS.

   - Extended kmalloc() alignment guarantees (Vlastimil Babka)

     For years now we have guaranteed natural alignment for power-of-two
     allocations, but nothing was defined for other sizes (in practice,
     we have two such buckets, kmalloc-96 and kmalloc-192).

     To avoid unnecessary padding in the rust layer due to its alignment
     rules, extend the guarantee so that the alignment is at least the
     largest power-of-two divisor of the requested size.

     This fits what rust needs, is a superset of the existing
     power-of-two guarantee, and does not in practice change the layout
     (and thus does not add overhead due to padding) of the kmalloc-96
     and kmalloc-192 caches, unless slab debugging is enabled for them.

   - Cleanups and non-critical fixups (Chengming Zhou, Suren
     Baghdasaryan, Matthew Willcox, Alex Shi, and Vlastimil Babka)

     Various tweaks related to the new alloc profiling code, folio
     conversion, debugging and more leftovers after SLAB"

Link: https://lore.kernel.org/all/20240701190152.it.631-kees@kernel.org/ [1]

* tag 'slab-for-6.11' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab:
  mm/memcg: alignment memcg_data define condition
  mm, slab: move prepare_slab_obj_exts_hook under CONFIG_MEM_ALLOC_PROFILING
  mm, slab: move allocation tagging code in the alloc path into a hook
  mm/util: Use dedicated slab buckets for memdup_user()
  ipc, msg: Use dedicated slab buckets for alloc_msg()
  mm/slab: Introduce kmem_buckets_create() and family
  mm/slab: Introduce kvmalloc_buckets_node() that can take kmem_buckets argument
  mm/slab: Plumb kmem_buckets into __do_kmalloc_node()
  mm/slab: Introduce kmem_buckets typedef
  slab, rust: extend kmalloc() alignment guarantees to remove Rust padding
  slab: delete useless RED_INACTIVE and RED_ACTIVE
  slab: don't put freepointer outside of object if only orig_size
  slab: make check_object() more consistent
  mm: Reduce the number of slab->folio casts
  mm, slab: don't wrap internal functions with alloc_hooks()

1 files changed, 6 insertions, 13 deletions

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 229642960cd1..e6ea601f38c6 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -18,23 +18,16 @@ pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: F
     // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
     let layout = new_layout.pad_to_align();
 
-    let mut size = layout.size();
-
-    if layout.align() > bindings::ARCH_SLAB_MINALIGN {
-        // The alignment requirement exceeds the slab guarantee, thus try to enlarge the size
-        // to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for
-        // more information).
-        //
-        // Note that `layout.size()` (after padding) is guaranteed to be a multiple of
-        // `layout.align()`, so `next_power_of_two` gives enough alignment guarantee.
-        size = size.next_power_of_two();
-    }
+    // Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
+    // which together with the slab guarantees means the `krealloc` will return a properly aligned
+    // object (see comments in `kmalloc()` for more information).
+    let size = layout.size();
 
     // SAFETY:
     // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
     //   function safety requirement.
-    // - `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero
-    //   according to the function safety requirement) or a result from `next_power_of_two()`.
+    // - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
+    //   to the function safety requirement)
     unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
 }