Commit 603b4416 authored by KP Singh's avatar KP Singh Committed by Alexei Starovoitov
Browse files

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: default avatarKP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/r/20250914215141.15144-2-kpsingh@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 3547a61e

include/linux/bpf.h

+5 −1
Original line number Diff line number Diff line
@@ -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 */

	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,

kernel/bpf/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -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

kernel/bpf/core.c

+2 −3
Original line number Diff line number Diff line
@@ -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;

}