bpf: Update the bpf_prog_calc_tag to use SHA256

Exclusive maps restrict map access to specific programs using a hash.
The current hash used for this is SHA1, which is prone to collisions.
This patch uses SHA256, which  is more resilient against
collisions. This new hash is stored in bpf_prog and used by the verifier
to determine if a program can access a given exclusive map.

The original 64-bit tags are kept, as they are used by users as a short,
possibly colliding program identifier for non-security purposes.

Signed-off-by: KP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/r/20250914215141.15144-2-kpsingh@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 41f776071ff51797419a82375121b6de57924d5c..d75902074bd1f3375ee7fd97fe8aafdbb642da9c 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -31,6 +31,7 @@
 #include <linux/memcontrol.h>
 #include <linux/cfi.h>
 #include <asm/rqspinlock.h>
+#include <crypto/sha2.h>
 
 struct bpf_verifier_env;
 struct bpf_verifier_log;
@@ -1717,7 +1718,10 @@ struct bpf_prog {
        enum bpf_attach_type    expected_attach_type; /* For some prog types */
        u32                     len;            /* Number of filter blocks */
        u32                     jited_len;      /* Size of jited insns in bytes */
-       u8                      tag[BPF_TAG_SIZE];
+       union {
+               u8 digest[SHA256_DIGEST_SIZE];
+               u8 tag[BPF_TAG_SIZE];
+       };
        struct bpf_prog_stats __percpu *stats;
        int __percpu            *active;
        unsigned int            (*bpf_func)(const void *ctx,

diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index 17067dcb43861006c35015a577878a2b96d74b28..eb3de35734f09222afc136fe7f3931954b64bc46 100644 (file)
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -3,7 +3,7 @@
 # BPF interpreter that, for example, classic socket filters depend on.
 config BPF
        bool
-       select CRYPTO_LIB_SHA1
+       select CRYPTO_LIB_SHA256
 
 # Used by archs to tell that they support BPF JIT compiler plus which
 # flavour. Only one of the two can be selected for a specific arch since

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 1cda2589d4b35cdf09f7dd8e0c992ef09e20a1a3..9b64674df16b88c2b88077a242fbe440c1bbe954 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -39,6 +39,7 @@
 #include <linux/bpf_mem_alloc.h>
 #include <linux/memcontrol.h>
 #include <linux/execmem.h>
+#include <crypto/sha2.h>
 
 #include <asm/barrier.h>
 #include <linux/unaligned.h>
@@ -296,7 +297,6 @@ void __bpf_prog_free(struct bpf_prog *fp)
 int bpf_prog_calc_tag(struct bpf_prog *fp)
 {
        size_t size = bpf_prog_insn_size(fp);
-       u8 digest[SHA1_DIGEST_SIZE];
        struct bpf_insn *dst;
        bool was_ld_map;
        u32 i;
@@ -327,8 +327,7 @@ int bpf_prog_calc_tag(struct bpf_prog *fp)
                        was_ld_map = false;
                }
        }
-       sha1((const u8 *)dst, size, digest);
-       memcpy(fp->tag, digest, sizeof(fp->tag));
+       sha256((u8 *)dst, size, fp->digest);
        vfree(dst);
        return 0;
 }