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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 <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.