On Thu, Mar 18, 2021 at 11:31 AM Nick Desaulniers
<ndesaulniers@xxxxxxxxxx> wrote:
>
> On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
> >
> > Casting the comparison function to a different type trips indirect
> > call Control-Flow Integrity (CFI) checking. Remove the additional
> > consts from cmp_func, and the now unneeded casts.
> >
> > Fixes: 043b3f7b6388 ("lib/list_sort: simplify and remove MAX_LIST_LENGTH_BITS")
> > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> > lib/list_sort.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/lib/list_sort.c b/lib/list_sort.c
> > index 52f0c258c895..b14accf4ef83 100644
> > --- a/lib/list_sort.c
> > +++ b/lib/list_sort.c
> > @@ -8,7 +8,7 @@
> > #include <linux/list.h>
> >
> > typedef int __attribute__((nonnull(2,3))) (*cmp_func)(void *,
> > - struct list_head const *, struct list_head const *);
> > + struct list_head *, struct list_head *);
> >
> > /*
> > * Returns a list organized in an intermediate format suited
> > @@ -227,7 +227,7 @@ void list_sort(void *priv, struct list_head *head,
>
> There's definitely some const confusion going on around here.
> Comparison functions that modify their in/out parameters are a code
> smell, and I wonder if any exist in tree?
>
> I think it would be better to enforce one signature for cmp_func
> throughout lib/list_sort.c and the tree, either const or not, but not
> a mix of both. I know `const` is messy because it tends to propagate
> everywhere, so I don't care which is preferred (making cmp_func have
> const qualified params or not, though if we're already being pedantic
> about which params are non-null...), but something like this might be
> nicer:
Sure, an alternative to removing the internal casts is to actually
change all the callers to use a comparison function with const
parameters. That's quite a bit more invasive, but I'm fine with that
approach too.
>
> ```
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index 5132f64a5cee..d475b3cfd06f 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -75,7 +75,8 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
> blk_mq_run_hw_queue(hctx, true);
> }
>
> -static int sched_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
> +static int sched_rq_cmp(void *priv, const struct list_head *a,
> + const struct list_head *b)
> {
> struct request *rqa = container_of(a, struct request, queuelist);
> struct request *rqb = container_of(b, struct request, queuelist);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2e825a7a3606..9ed063ffdb27 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1905,7 +1905,8 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx
> *hctx, struct blk_mq_ctx *ctx,
> spin_unlock(&ctx->lock);
> }
>
> -static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
> +static int plug_rq_cmp(void *priv, const struct list_head *a,
> + const struct list_head *b)
> {
> struct request *rqa = container_of(a, struct request, queuelist);
> struct request *rqb = container_of(b, struct request, queuelist);
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 1ac67d4505e0..5a3a343499f6 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1290,7 +1290,8 @@ EXPORT_SYMBOL(drm_mode_prune_invalid);
> * Negative if @lh_a is better than @lh_b, zero if they're equivalent, or
> * positive if @lh_b is better than @lh_a.
> */
> -static int drm_mode_compare(void *priv, struct list_head *lh_a,
> struct list_head *lh_b)
> +static int drm_mode_compare(void *priv, const struct list_head *lh_a,
> + const struct list_head *lh_b)
> {
> struct drm_display_mode *a = list_entry(lh_a, struct
> drm_display_mode, head);
> struct drm_display_mode *b = list_entry(lh_b, struct
> drm_display_mode, head);
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.c
> b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> index 34e6096f196e..7586dffd27d3 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_user.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> @@ -49,7 +49,8 @@ static const u8 uabi_classes[] = {
> [VIDEO_ENHANCEMENT_CLASS] = I915_ENGINE_CLASS_VIDEO_ENHANCE,
> };
>
> -static int engine_cmp(void *priv, struct list_head *A, struct list_head *B)
> +static int engine_cmp(void *priv, const struct list_head *A,
> + const struct list_head *B)
> {
> const struct intel_engine_cs *a =
> container_of((struct rb_node *)A, typeof(*a), uabi_node);
> diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
> index 4c2a9fe30067..4493ef0c715e 100644
> --- a/fs/ext4/fsmap.c
> +++ b/fs/ext4/fsmap.c
> @@ -354,8 +354,8 @@ static unsigned int ext4_getfsmap_find_sb(struct
> super_block *sb,
>
> /* Compare two fsmap items. */
> static int ext4_getfsmap_compare(void *priv,
> - struct list_head *a,
> - struct list_head *b)
> + const struct list_head *a,
> + const struct list_head *b)
> {
> struct ext4_fsmap *fa;
> struct ext4_fsmap *fb;
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 414769a6ad11..0129e6bab985 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1155,7 +1155,8 @@ iomap_ioend_try_merge(struct iomap_ioend *ioend,
> struct list_head *more_ioends,
> EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);
>
> static int
> -iomap_ioend_compare(void *priv, struct list_head *a, struct list_head *b)
> +iomap_ioend_compare(void *priv, const struct list_head *a,
> + const struct list_head *b)
> {
> struct iomap_ioend *ia = container_of(a, struct iomap_ioend, io_list);
> struct iomap_ioend *ib = container_of(b, struct iomap_ioend, io_list);
> diff --git a/include/linux/list_sort.h b/include/linux/list_sort.h
> index 20f178c24e9d..4fe9cb94d0d1 100644
> --- a/include/linux/list_sort.h
> +++ b/include/linux/list_sort.h
> @@ -6,8 +6,9 @@
>
> struct list_head;
>
> +typedef int __attribute__((nonnull(2,3))) (*cmp_func)(void *,
> + struct list_head const *, struct list_head const *);
> +
Note that we already have cmp_func_t in linux/types.h, so something
like list_cmp_func_t would probably be more appropriate here.
> __attribute__((nonnull(2,3)))
> -void list_sort(void *priv, struct list_head *head,
> - int (*cmp)(void *priv, struct list_head *a,
> - struct list_head *b));
> +void list_sort(void *priv, struct list_head *head, cmp_func cmp);
> #endif
> diff --git a/lib/list_sort.c b/lib/list_sort.c
> index 52f0c258c895..6cfac649c4a6 100644
> --- a/lib/list_sort.c
> +++ b/lib/list_sort.c
> @@ -7,9 +7,6 @@
> #include <linux/list_sort.h>
> #include <linux/list.h>
>
> -typedef int __attribute__((nonnull(2,3))) (*cmp_func)(void *,
> - struct list_head const *, struct list_head const *);
> -
> /*
> * Returns a list organized in an intermediate format suited
> * to chaining of merge() calls: null-terminated, no reserved or
> @@ -185,9 +182,7 @@ static void merge_final(void *priv, cmp_func cmp,
> struct list_head *head,
> * 2^(k+1) - 1 (second merge of case 5 when x == 2^(k-1) - 1).
> */
> __attribute__((nonnull(2,3)))
> -void list_sort(void *priv, struct list_head *head,
> - int (*cmp)(void *priv, struct list_head *a,
> - struct list_head *b))
> +void list_sort(void *priv, struct list_head *head, cmp_func cmp)
> {
> struct list_head *list = head->next, *pending = NULL;
> size_t count = 0; /* Count of pending */
> ```
> There are probably more instances in the tree to clean up, but that
> compiles with x86_64 defconfig, and I'm sure it doesn't suffer the CFI
> issue from the cast.
You indeed missed some callers, but after fixing all the remaining
ones too, arm64 and x86_64 allyesconfigs still seem to build just fine
for me:
arch/arm64/kvm/vgic/vgic-its.c | 8 ++++----
arch/arm64/kvm/vgic/vgic.c | 2 +-
block/blk-mq-sched.c | 2 +-
block/blk-mq.c | 2 +-
drivers/acpi/nfit/core.c | 2 +-
drivers/acpi/numa/hmat.c | 2 +-
drivers/clk/keystone/sci-clk.c | 4 ++--
drivers/gpu/drm/drm_modes.c | 2 +-
drivers/gpu/drm/i915/gt/intel_engine_user.c | 2 +-
drivers/gpu/drm/i915/gvt/debugfs.c | 2 +-
drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 2 +-
drivers/gpu/drm/radeon/radeon_cs.c | 4 ++--
drivers/infiniband/hw/usnic/usnic_uiom_interval_tree.c | 2 +-
drivers/interconnect/qcom/bcm-voter.c | 2 +-
drivers/md/raid5.c | 2 +-
drivers/misc/sram.c | 4 ++--
drivers/nvme/host/core.c | 2 +-
drivers/pci/controller/cadence/pcie-cadence-host.c | 3 ++-
drivers/spi/spi-loopback-test.c | 2 +-
fs/btrfs/raid56.c | 2 +-
fs/btrfs/tree-log.c | 2 +-
fs/btrfs/volumes.c | 2 +-
fs/ext4/fsmap.c | 4 ++--
fs/gfs2/glock.c | 2 +-
fs/gfs2/log.c | 2 +-
fs/gfs2/lops.c | 2 +-
fs/iomap/buffered-io.c | 2 +-
fs/ubifs/gc.c | 6 +++---
fs/ubifs/replay.c | 4 ++--
fs/xfs/scrub/bitmap.c | 4 ++--
fs/xfs/xfs_bmap_item.c | 4 ++--
fs/xfs/xfs_buf.c | 4 ++--
fs/xfs/xfs_extent_busy.c | 4 ++--
fs/xfs/xfs_extent_busy.h | 2 +-
fs/xfs/xfs_extfree_item.c | 4 ++--
fs/xfs/xfs_refcount_item.c | 4 ++--
fs/xfs/xfs_rmap_item.c | 4 ++--
include/linux/list_sort.h | 7 ++++---
lib/list_sort.c | 17 ++++++-----------
lib/test_list_sort.c | 2 +-
net/tipc/name_table.c | 4 ++--
41 files changed, 68 insertions(+), 71 deletions(-)
I'll have to double check that all the affected code is actually
included in these builds, but if nobody objects and I don't run into
any issues, I'll include the patch in v3.
Sami
