From 60a3b2253c413cf601783b070507d7dd6620c954 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Tue, 2 Sep 2014 22:53:44 +0200 Subject: net: bpf: make eBPF interpreter images read-only With eBPF getting more extended and exposure to user space is on it's way, hardening the memory range the interpreter uses to steer its command flow seems appropriate. This patch moves the to be interpreted bytecode to read-only pages. In case we execute a corrupted BPF interpreter image for some reason e.g. caused by an attacker which got past a verifier stage, it would not only provide arbitrary read/write memory access but arbitrary function calls as well. After setting up the BPF interpreter image, its contents do not change until destruction time, thus we can setup the image on immutable made pages in order to mitigate modifications to that code. The idea is derived from commit 314beb9bcabf ("x86: bpf_jit_comp: secure bpf jit against spraying attacks"). This is possible because bpf_prog is not part of sk_filter anymore. After setup bpf_prog cannot be altered during its life-time. This prevents any modifications to the entire bpf_prog structure (incl. function/JIT image pointer). Every eBPF program (including classic BPF that are migrated) have to call bpf_prog_select_runtime() to select either interpreter or a JIT image as a last setup step, and they all are being freed via bpf_prog_free(), including non-JIT. Therefore, we can easily integrate this into the eBPF life-time, plus since we directly allocate a bpf_prog, we have no performance penalty. Tested with seccomp and test_bpf testsuite in JIT/non-JIT mode and manual inspection of kernel_page_tables. Brad Spengler proposed the same idea via Twitter during development of this patch. Joint work with Hannes Frederic Sowa. Suggested-by: Brad Spengler Signed-off-by: Daniel Borkmann Signed-off-by: Hannes Frederic Sowa Cc: Alexei Starovoitov Cc: Kees Cook Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- arch/powerpc/net/bpf_jit_comp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 3afa6f4c1957..40c53ff59124 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -697,5 +697,6 @@ void bpf_jit_free(struct bpf_prog *fp) { if (fp->jited) module_free(NULL, fp->bpf_func); - kfree(fp); + + bpf_prog_unlock_free(fp); } -- cgit v1.2.3 From 286aad3c4014ca825c447e07e24f8929e6d266d2 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 8 Sep 2014 08:04:49 +0200 Subject: net: bpf: be friendly to kmemcheck Reported by Mikulas Patocka, kmemcheck currently barks out a false positive since we don't have special kmemcheck annotation for bitfields used in bpf_prog structure. We currently have jited:1, len:31 and thus when accessing len while CONFIG_KMEMCHECK enabled, kmemcheck throws a warning that we're reading uninitialized memory. As we don't need the whole bit universe for pages member, we can just split it to u16 and use a bool flag for jited instead of a bitfield. Signed-off-by: Mikulas Patocka Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- arch/powerpc/net/bpf_jit_comp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 40c53ff59124..cbae2dfd053c 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -686,7 +686,7 @@ void bpf_jit_compile(struct bpf_prog *fp) ((u64 *)image)[0] = (u64)code_base; ((u64 *)image)[1] = local_paca->kernel_toc; fp->bpf_func = (void *)image; - fp->jited = 1; + fp->jited = true; } out: kfree(addrs); -- cgit v1.2.3