path: root/lib
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authorAlexei Starovoitov <ast@kernel.org>2018-01-09 10:04:29 -0800
committerDaniel Borkmann <daniel@iogearbox.net>2018-01-09 22:25:26 +0100
commit290af86629b25ffd1ed6232c4e9107da031705cb (patch)
tree0d4c514627f1b748a9a8887b5386290b9d140fc0 /lib
parentbe95a845cc4402272994ce290e3ad928aff06cb9 (diff)
bpf: introduce BPF_JIT_ALWAYS_ON config
The BPF interpreter has been used as part of the spectre 2 attack CVE-2017-5715. A quote from goolge project zero blog: "At this point, it would normally be necessary to locate gadgets in the host kernel code that can be used to actually leak data by reading from an attacker-controlled location, shifting and masking the result appropriately and then using the result of that as offset to an attacker-controlled address for a load. But piecing gadgets together and figuring out which ones work in a speculation context seems annoying. So instead, we decided to use the eBPF interpreter, which is built into the host kernel - while there is no legitimate way to invoke it from inside a VM, the presence of the code in the host kernel's text section is sufficient to make it usable for the attack, just like with ordinary ROP gadgets." To make attacker job harder introduce BPF_JIT_ALWAYS_ON config option that removes interpreter from the kernel in favor of JIT-only mode. So far eBPF JIT is supported by: x64, arm64, arm32, sparc64, s390, powerpc64, mips64 The start of JITed program is randomized and code page is marked as read-only. In addition "constant blinding" can be turned on with net.core.bpf_jit_harden v2->v3: - move __bpf_prog_ret0 under ifdef (Daniel) v1->v2: - fix init order, test_bpf and cBPF (Daniel's feedback) - fix offloaded bpf (Jakub's feedback) - add 'return 0' dummy in case something can invoke prog->bpf_func - retarget bpf tree. For bpf-next the patch would need one extra hunk. It will be sent when the trees are merged back to net-next Considered doing: int bpf_jit_enable __read_mostly = BPF_EBPF_JIT_DEFAULT; but it seems better to land the patch as-is and in bpf-next remove bpf_jit_enable global variable from all JITs, consolidate in one place and remove this jit_init() function. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'lib')
1 files changed, 7 insertions, 4 deletions
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 9e9748089270..f369889e521d 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -6250,9 +6250,8 @@ static struct bpf_prog *generate_filter(int which, int *err)
return NULL;
- /* We don't expect to fail. */
if (*err) {
- pr_cont("FAIL to attach err=%d len=%d\n",
+ pr_cont("FAIL to prog_create err=%d len=%d\n",
*err, fprog.len);
return NULL;
@@ -6276,6 +6275,10 @@ static struct bpf_prog *generate_filter(int which, int *err)
* checks.
fp = bpf_prog_select_runtime(fp, err);
+ if (*err) {
+ pr_cont("FAIL to select_runtime err=%d\n", *err);
+ return NULL;
+ }
@@ -6461,8 +6464,8 @@ static __init int test_bpf(void)
- return err;
+ err_cnt++;
+ continue;
pr_cont("jited:%u ", fp->jited);