ebpf: Allow dereferences of PTR_TO_STACK registers
mov %rsp, %r1 ; r1 = rsp
add $-8, %r1 ; r1 = rsp - 8
store_q $123, -8(%rsp) ; *(u64*)r1 = 123 <- valid
store_q $123, (%r1) ; *(u64*)r1 = 123 <- previously invalid
mov $0, %r0
exit ; Always need to exit
And we'd get the following error:
0: (bf) r1 = r10
1: (07) r1 += -8
2: (7a) *(u64 *)(r10 -8) = 999
3: (7a) *(u64 *)(r1 +0) = 999
R1 invalid mem access 'fp'
Unable to load program
We already know that a register is a stack address and the appropriate
offset, so we should be able to validate those references as well.
Signed-off-by: Alex Gartrell <agartrell@fb.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 039d866..cd307df 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -648,6 +648,9 @@
struct verifier_state *state = &env->cur_state;
int size, err = 0;
+ if (state->regs[regno].type == PTR_TO_STACK)
+ off += state->regs[regno].imm;
+
size = bpf_size_to_bytes(bpf_size);
if (size < 0)
return size;
@@ -667,7 +670,8 @@
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown_value(state->regs, value_regno);
- } else if (state->regs[regno].type == FRAME_PTR) {
+ } else if (state->regs[regno].type == FRAME_PTR ||
+ state->regs[regno].type == PTR_TO_STACK) {
if (off >= 0 || off < -MAX_BPF_STACK) {
verbose("invalid stack off=%d size=%d\n", off, size);
return -EACCES;