From 1411707acb85c514c603f692327c98db48127900 Mon Sep 17 00:00:00 2001 From: Thomas Graf Date: Tue, 18 Oct 2016 19:51:19 +0200 Subject: bpf: Detect identical PTR_TO_MAP_VALUE_OR_NULL registers [ Upstream commit 57a09bf0a416700676e77102c28f9cfcb48267e0 ] A BPF program is required to check the return register of a map_elem_lookup() call before accessing memory. The verifier keeps track of this by converting the type of the result register from PTR_TO_MAP_VALUE_OR_NULL to PTR_TO_MAP_VALUE after a conditional jump ensures safety. This check is currently exclusively performed for the result register 0. In the event the compiler reorders instructions, BPF_MOV64_REG instructions may be moved before the conditional jump which causes them to keep their type PTR_TO_MAP_VALUE_OR_NULL to which the verifier objects when the register is accessed: 0: (b7) r1 = 10 1: (7b) *(u64 *)(r10 -8) = r1 2: (bf) r2 = r10 3: (07) r2 += -8 4: (18) r1 = 0x59c00000 6: (85) call 1 7: (bf) r4 = r0 8: (15) if r0 == 0x0 goto pc+1 R0=map_value(ks=8,vs=8) R4=map_value_or_null(ks=8,vs=8) R10=fp 9: (7a) *(u64 *)(r4 +0) = 0 R4 invalid mem access 'map_value_or_null' This commit extends the verifier to keep track of all identical PTR_TO_MAP_VALUE_OR_NULL registers after a map_elem_lookup() by assigning them an ID and then marking them all when the conditional jump is observed. Signed-off-by: Thomas Graf Reviewed-by: Josef Bacik Acked-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/bpf_verifier.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 6aaf425cebc3..7453c1281531 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -24,13 +24,13 @@ struct bpf_reg_state { */ s64 min_value; u64 max_value; + u32 id; union { /* valid when type == CONST_IMM | PTR_TO_STACK | UNKNOWN_VALUE */ s64 imm; /* valid when type == PTR_TO_PACKET* */ struct { - u32 id; u16 off; u16 range; }; -- cgit v1.2.3