Commit b7552e1b authored May 18, 2016 by Daniel Borkmann Committed by David S. Miller May 20, 2016

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 <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 09ec8e7f

kernel/bpf/core.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);

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