On Thu, Jan 17, 2019 at 04:34:45PM +0100, Daniel Borkmann wrote:
> During review I noticed that inner meta map setup for map in
> map is buggy in that it does not propagate all needed data
> from the reference map which the verifier is later accessing.
>
> In particular one such case is index masking to prevent out of
> bounds access under speculative execution due to missing the
> map's unpriv_array/index_mask field propagation. Fix this such
> that the verifier is generating the correct code for inlined
> lookups in case of unpriviledged use.
>
> Before patch (test_verifier's 'map in map access' dump):
>
> # bpftool prog dump xla id 3
> 0: (62) *(u32 *)(r10 -4) = 0
> 1: (bf) r2 = r10
> 2: (07) r2 += -4
> 3: (18) r1 = map[id:4]
> 5: (07) r1 += 272 |
> 6: (61) r0 = *(u32 *)(r2 +0) |
> 7: (35) if r0 >= 0x1 goto pc+6 | Inlined map in map lookup
> 8: (54) (u32) r0 &= (u32) 0 | with index masking for
> 9: (67) r0 <<= 3 | map->unpriv_array.
> 10: (0f) r0 += r1 |
> 11: (79) r0 = *(u64 *)(r0 +0) |
> 12: (15) if r0 == 0x0 goto pc+1 |
> 13: (05) goto pc+1 |
> 14: (b7) r0 = 0 |
> 15: (15) if r0 == 0x0 goto pc+11
> 16: (62) *(u32 *)(r10 -4) = 0
> 17: (bf) r2 = r10
> 18: (07) r2 += -4
> 19: (bf) r1 = r0
> 20: (07) r1 += 272 |
> 21: (61) r0 = *(u32 *)(r2 +0) | Index masking missing (!)
> 22: (35) if r0 >= 0x1 goto pc+3 | for inner map despite
> 23: (67) r0 <<= 3 | map->unpriv_array set.
> 24: (0f) r0 += r1 |
> 25: (05) goto pc+1 |
> 26: (b7) r0 = 0 |
> 27: (b7) r0 = 0
> 28: (95) exit
>
> After patch:
>
> # bpftool prog dump xla id 1
> 0: (62) *(u32 *)(r10 -4) = 0
> 1: (bf) r2 = r10
> 2: (07) r2 += -4
> 3: (18) r1 = map[id:2]
> 5: (07) r1 += 272 |
> 6: (61) r0 = *(u32 *)(r2 +0) |
> 7: (35) if r0 >= 0x1 goto pc+6 | Same inlined map in map lookup
> 8: (54) (u32) r0 &= (u32) 0 | with index masking due to
> 9: (67) r0 <<= 3 | map->unpriv_array.
> 10: (0f) r0 += r1 |
> 11: (79) r0 = *(u64 *)(r0 +0) |
> 12: (15) if r0 == 0x0 goto pc+1 |
> 13: (05) goto pc+1 |
> 14: (b7) r0 = 0 |
> 15: (15) if r0 == 0x0 goto pc+12
> 16: (62) *(u32 *)(r10 -4) = 0
> 17: (bf) r2 = r10
> 18: (07) r2 += -4
> 19: (bf) r1 = r0
> 20: (07) r1 += 272 |
> 21: (61) r0 = *(u32 *)(r2 +0) |
> 22: (35) if r0 >= 0x1 goto pc+4 | Now fixed inlined inner map
> 23: (54) (u32) r0 &= (u32) 0 | lookup with proper index masking
> 24: (67) r0 <<= 3 | for map->unpriv_array.
> 25: (0f) r0 += r1 |
> 26: (05) goto pc+1 |
> 27: (b7) r0 = 0 |
> 28: (b7) r0 = 0
> 29: (95) exit
>
> Fixes: b2157399cc98 ("bpf: prevent out-of-bounds speculation")
> Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
The fix looks great. Thanks for the fix!
In the future if there is another exception other than
array_map, a inner_map->ops->map_meta_alloc() can be introduced?
Acked-by: Martin KaFai Lau <ka...@fb.com>
