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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>
This commit is contained in:
KP Singh 2025-09-14 23:51:30 +02:00 committed by Alexei Starovoitov
parent 3547a61ee2
commit 603b441623
3 changed files with 8 additions and 5 deletions
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6
include/linux/bpf.h
View File

@ -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,

2
kernel/bpf/Kconfig
View File

@ -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

5
kernel/bpf/core.c
View File

@ -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;
}