mm/bpf: Add bpf_get_kmem_cache() kfunc

The bpf_get_kmem_cache() is to get a slab cache information from a
virtual address like virt_to_cache().  If the address is a pointer
to a slab object, it'd return a valid kmem_cache pointer, otherwise
NULL is returned.

It doesn't grab a reference count of the kmem_cache so the caller is
responsible to manage the access.  The returned point is marked as
PTR_UNTRUSTED.

The intended use case for now is to symbolize locks in slab objects
from the lock contention tracepoints.

Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev> (mm/*)
Acked-by: Vlastimil Babka <vbabka@suse.cz> #mm/slab
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20241010232505.1339892-3-namhyung@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 4053f279ed4cc7ab4141e99d9387273daa0a24a0..aaaefefdf692b839470d6643b4355f717af37edc 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3090,6 +3090,7 @@ BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_get_kmem_cache)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cfc62e0776bff2c84b1292d228781941e2c33cef..f514247ba8ba8a579ef39f15ab0c585db36828b9 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11259,6 +11259,7 @@ enum special_kfunc_type {
        KF_bpf_preempt_enable,
        KF_bpf_iter_css_task_new,
        KF_bpf_session_cookie,
+       KF_bpf_get_kmem_cache,
 };
 
 BTF_SET_START(special_kfunc_set)
@@ -11324,6 +11325,7 @@ BTF_ID(func, bpf_session_cookie)
 #else
 BTF_ID_UNUSED
 #endif
+BTF_ID(func, bpf_get_kmem_cache)
 
 static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
 {
@@ -12834,6 +12836,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
                        regs[BPF_REG_0].type = PTR_TO_BTF_ID;
                        regs[BPF_REG_0].btf_id = ptr_type_id;
 
+                       if (meta.func_id == special_kfunc_list[KF_bpf_get_kmem_cache])
+                               regs[BPF_REG_0].type |= PTR_UNTRUSTED;
+
                        if (is_iter_next_kfunc(&meta)) {
                                struct bpf_reg_state *cur_iter;
 

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 7443244656150325fb2a7d0158a71821e1418062..f97a95289562a37bcddb0a5e24ffe51e7ae6e61a 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1322,6 +1322,25 @@ size_t ksize(const void *objp)
 }
 EXPORT_SYMBOL(ksize);
 
+#ifdef CONFIG_BPF_SYSCALL
+#include <linux/btf.h>
+
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc struct kmem_cache *bpf_get_kmem_cache(u64 addr)
+{
+       struct slab *slab;
+
+       if (!virt_addr_valid((void *)(long)addr))
+               return NULL;
+
+       slab = virt_to_slab((void *)(long)addr);
+       return slab ? slab->slab_cache : NULL;
+}
+
+__bpf_kfunc_end_defs();
+#endif /* CONFIG_BPF_SYSCALL */
+
 /* Tracepoints definitions. */
 EXPORT_TRACEPOINT_SYMBOL(kmalloc);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);