On 05/01/18 23:02, Alexei Starovoitov wrote:
> since commit 82abbf8d2fc4 the verifier rejects the bit-wise
> arithmetic on pointers earlier.
> The test 'dubious pointer arithmetic' now has less output to match on.
> Adjust it.
>
> Fixes: 82abbf8d2fc4 ("bpf: do not allow root to mangle valid pointers")
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Alexei Starovoitov <[email protected]>
> ---
> tools/testing/selftests/bpf/test_align.c | 22 +---------------------
> 1 file changed, 1 insertion(+), 21 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/test_align.c
> b/tools/testing/selftests/bpf/test_align.c
> index 8591c89c0828..471bbbdb94db 100644
> --- a/tools/testing/selftests/bpf/test_align.c
> +++ b/tools/testing/selftests/bpf/test_align.c
> @@ -474,27 +474,7 @@ static struct bpf_align_test tests[] = {
> .result = REJECT,
> .matches = {
> {4, "R5=pkt(id=0,off=0,r=0,imm=0)"},
> - /* ptr & 0x40 == either 0 or 0x40 */
> - {5, "R5=inv(id=0,umax_value=64,var_off=(0x0; 0x40))"},
> - /* ptr << 2 == unknown, (4n) */
> - {7,
> "R5=inv(id=0,smax_value=9223372036854775804,umax_value=18446744073709551612,var_off=(0x0;
> 0xfffffffffffffffc))"},
> - /* (4n) + 14 == (4n+2). We blow our bounds, because
> - * the add could overflow.
> - */
> - {8, "R5=inv(id=0,var_off=(0x2; 0xfffffffffffffffc))"},
> - /* Checked s>=0 */
> - {10,
> "R5=inv(id=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2;
> 0x7ffffffffffffffc))"},
> - /* packet pointer + nonnegative (4n+2) */
> - {12,
> "R6=pkt(id=1,off=0,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2;
> 0x7ffffffffffffffc))"},
> - {14,
> "R4=pkt(id=1,off=4,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2;
> 0x7ffffffffffffffc))"},
> - /* NET_IP_ALIGN + (4n+2) == (4n), alignment is fine.
> - * We checked the bounds, but it might have been able
> - * to overflow if the packet pointer started in the
> - * upper half of the address space.
> - * So we did not get a 'range' on R6, and the access
> - * attempt will fail.
> - */
> - {16,
> "R6=pkt(id=1,off=0,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2;
> 0x7ffffffffffffffc))"},
> + /* R5 bitwise operator &= on pointer prohibited */
> }
> },
> {
Rather than neutering this test, we should change it to keep the part where
it tests that a large pkt_ptr offset prevents us getting a reg->range.
Specifically, in this test we have
r2 = pkt
r5 = large unknown scalar
r6 = r2 + r5
r4 = r6 + 4
Then we check r4 < pkt_end, which normally would give r6->range = 4, but in
this case must not do so since r6 could be (u64)(-2) in which case r4 = 2
< pkt_end despite r6 not pointing into the packet.
AFAICT there is not other coverage of this case in test_align, and I don't
recall such a test being in test_verifier either. So please instead replace
the insns that do prohibited ops on pointers with some other way of creating
a large unknown scalar, and keep the rest of the test case intact.
-Ed
