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authorJann Horn <jannh@google.com>2018-03-19 17:55:52 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-03-22 09:23:32 +0100
commita6132276ab5dcc38b3299082efeb25b948263adb (patch)
treef7634be69b51ae5ba67e10d4786566c100f73717
parent5a876e8742b709ed4d3db068fe453515609e0402 (diff)
bpf: fix incorrect sign extension in check_alu_op()
commit 95a762e2c8c942780948091f8f2a4f32fce1ac6f upstream. Distinguish between BPF_ALU64|BPF_MOV|BPF_K (load 32-bit immediate, sign-extended to 64-bit) and BPF_ALU|BPF_MOV|BPF_K (load 32-bit immediate, zero-padded to 64-bit); only perform sign extension in the first case. This patch differs from the mainline one because the verifier's internals have changed in the meantime. Mainline tracks register values as 64-bit values; however, 4.4 still stores tracked register values as 32-bit values with sign extension. Therefore, in the case of a 32-bit op with negative immediate, the value can't be tracked; leave the register as UNKNOWN_VALUE (set by the preceding check_reg_arg() call). I have manually tested this patch on top of 4.4.122. For the following BPF bytecode: BPF_MOV64_IMM(BPF_REG_1, 1), BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 1, 1), BPF_EXIT_INSN(), BPF_MOV32_IMM(BPF_REG_1, 1), BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 1, 1), BPF_EXIT_INSN(), BPF_MOV64_IMM(BPF_REG_1, -1), BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, -1, 1), BPF_EXIT_INSN(), BPF_MOV32_IMM(BPF_REG_1, -1), BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, -1, 2), BPF_MOV32_IMM(BPF_REG_0, 42), BPF_EXIT_INSN(), BPF_MOV32_IMM(BPF_REG_0, 43), BPF_EXIT_INSN() Verifier output on 4.4.122 without this patch: 0: (b7) r1 = 1 1: (15) if r1 == 0x1 goto pc+1 3: (b4) (u32) r1 = (u32) 1 4: (15) if r1 == 0x1 goto pc+1 6: (b7) r1 = -1 7: (15) if r1 == 0xffffffff goto pc+1 9: (b4) (u32) r1 = (u32) -1 10: (15) if r1 == 0xffffffff goto pc+2 13: (b4) (u32) r0 = (u32) 43 14: (95) exit Verifier output on 4.4.122+ with this patch: 0: (b7) r1 = 1 1: (15) if r1 == 0x1 goto pc+1 3: (b4) (u32) r1 = (u32) 1 4: (15) if r1 == 0x1 goto pc+1 6: (b7) r1 = -1 7: (15) if r1 == 0xffffffff goto pc+1 9: (b4) (u32) r1 = (u32) -1 10: (15) if r1 == 0xffffffff goto pc+2 R1=inv R10=fp 11: (b4) (u32) r0 = (u32) 42 12: (95) exit from 10 to 13: R1=imm-1 R10=fp 13: (b4) (u32) r0 = (u32) 43 14: (95) exit Signed-off-by: Jann Horn <jannh@google.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/bpf/verifier.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c14003840bc5..79e3c21a35d0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1135,7 +1135,8 @@ static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn)
regs[insn->dst_reg].type = UNKNOWN_VALUE;
regs[insn->dst_reg].map_ptr = NULL;
}
- } else {
+ } else if (BPF_CLASS(insn->code) == BPF_ALU64 ||
+ insn->imm >= 0) {
/* case: R = imm
* remember the value we stored into this reg
*/