From b7552e1bccbe3da9c8e7386c6188e8ea4667c8e7 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 18 May 2016 14:14:28 +0200 Subject: bpf: rather use get_random_int for randomizations Start address randomization and blinding in BPF currently use prandom_u32(). prandom_u32() values are not exposed to unpriviledged user space to my knowledge, but given other kernel facilities such as ASLR, stack canaries, etc make use of stronger get_random_int(), we better make use of it here as well given blinding requests successively new random values. get_random_int() has minimal entropy pool depletion, is not cryptographically secure, but doesn't need to be for our use cases here. Suggested-by: Hannes Frederic Sowa Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index f1e8a0d..b94a365 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -231,7 +231,7 @@ bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr, hdr->pages = size / PAGE_SIZE; hole = min_t(unsigned int, size - (proglen + sizeof(*hdr)), PAGE_SIZE - sizeof(*hdr)); - start = (prandom_u32() % hole) & ~(alignment - 1); + start = (get_random_int() % hole) & ~(alignment - 1); /* Leave a random number of instructions before BPF code. */ *image_ptr = &hdr->image[start]; @@ -251,7 +251,7 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, struct bpf_insn *to_buff) { struct bpf_insn *to = to_buff; - u32 imm_rnd = prandom_u32(); + u32 imm_rnd = get_random_int(); s16 off; BUILD_BUG_ON(BPF_REG_AX + 1 != MAX_BPF_JIT_REG); -- cgit v0.10.2