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authorDaniel Borkmann <daniel@iogearbox.net>2021-05-04 08:58:25 +0000
committerDaniel Borkmann <daniel@iogearbox.net>2021-05-25 22:08:53 +0200
commita7036191277f9fa68d92f2071ddc38c09b1e5ee5 (patch)
tree317ec094c6308d8326d11468976212bdb228dab9 /kernel/bpf/verifier.c
parentbb01a1bba579b4b1c5566af24d95f1767859771e (diff)
bpf: No need to simulate speculative domain for immediates
In 801c6058d14a ("bpf: Fix leakage of uninitialized bpf stack under speculation") we replaced masking logic with direct loads of immediates if the register is a known constant. Given in this case we do not apply any masking, there is also no reason for the operation to be truncated under the speculative domain. Therefore, there is also zero reason for the verifier to branch-off and simulate this case, it only needs to do it for unknown but bounded scalars. As a side-effect, this also enables few test cases that were previously rejected due to simulation under zero truncation. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Piotr Krysiuk <piotras@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/verifier.c')
-rw-r--r--kernel/bpf/verifier.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8574cb60915a..94ba5163d4c5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6545,8 +6545,12 @@ do_sim:
/* If we're in commit phase, we're done here given we already
* pushed the truncated dst_reg into the speculative verification
* stack.
+ *
+ * Also, when register is a known constant, we rewrite register-based
+ * operation to immediate-based, and thus do not need masking (and as
+ * a consequence, do not need to simulate the zero-truncation either).
*/
- if (commit_window)
+ if (commit_window || off_is_imm)
return 0;
/* Simulate and find potential out-of-bounds access under