On Tue, Jul 21, 2015 at 07:00:40PM -0700, Alex Gartrell wrote:
> 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
Is this your new eBPF assembler syntax? :)
imo gnu style looks ugly... ;)
It's great to see such in-depth understanding of verifier!!
> 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.
yes, we can teach verifier to do that.
Though llvm doesn't generate such code. It's small enough change.
> Signed-off-by: Alex Gartrell <agartr...@fb.com>
> ---
> kernel/bpf/verifier.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 039d866..5dfbece 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -676,6 +676,15 @@ static int check_mem_access(struct verifier_env *env,
> u32 regno, int off,
> err = check_stack_write(state, off, size, value_regno);
> else
> err = check_stack_read(state, off, size, value_regno);
> + } else if (state->regs[regno].type == PTR_TO_STACK) {
> + int real_off = state->regs[regno].imm + off;
real_off is missing alignment and bounds checks.
something like:
if (state->regs[regno].type == PTR_TO_STACK)
off += state->regs[regno].imm;
if (off % size != 0)
...
else if (state->regs[regno].type == FRAME_PTR || == PTR_TO_STACK)
.. as-is here ...
would fix it.
please add few accept and reject tests for this to test_verifier.c as well.
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