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author | Yonghong Song <yhs@fb.com> | 2018-04-28 22:28:11 -0700 |
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committer | Alexei Starovoitov <ast@kernel.org> | 2018-04-29 08:45:53 -0700 |
commit | 9cbe1f5a32dcd6d0508326f7d9098e5bc380a4fe (patch) | |
tree | 714686f3ad67476c1f58b86988bb9246d9064d67 /tools/testing/selftests/bpf/bpf_helpers.h | |
parent | bpf: remove never-hit branches in verifier adjust_scalar_min_max_vals (diff) | |
download | linux-dev-9cbe1f5a32dcd6d0508326f7d9098e5bc380a4fe.tar.xz linux-dev-9cbe1f5a32dcd6d0508326f7d9098e5bc380a4fe.zip |
bpf/verifier: improve register value range tracking with ARSH
When helpers like bpf_get_stack returns an int value
and later on used for arithmetic computation, the LSH and ARSH
operations are often required to get proper sign extension into
64-bit. For example, without this patch:
54: R0=inv(id=0,umax_value=800)
54: (bf) r8 = r0
55: R0=inv(id=0,umax_value=800) R8_w=inv(id=0,umax_value=800)
55: (67) r8 <<= 32
56: R8_w=inv(id=0,umax_value=3435973836800,var_off=(0x0; 0x3ff00000000))
56: (c7) r8 s>>= 32
57: R8=inv(id=0)
With this patch:
54: R0=inv(id=0,umax_value=800)
54: (bf) r8 = r0
55: R0=inv(id=0,umax_value=800) R8_w=inv(id=0,umax_value=800)
55: (67) r8 <<= 32
56: R8_w=inv(id=0,umax_value=3435973836800,var_off=(0x0; 0x3ff00000000))
56: (c7) r8 s>>= 32
57: R8=inv(id=0, umax_value=800,var_off=(0x0; 0x3ff))
With better range of "R8", later on when "R8" is added to other register,
e.g., a map pointer or scalar-value register, the better register
range can be derived and verifier failure may be avoided.
In our later example,
......
usize = bpf_get_stack(ctx, raw_data, max_len, BPF_F_USER_STACK);
if (usize < 0)
return 0;
ksize = bpf_get_stack(ctx, raw_data + usize, max_len - usize, 0);
......
Without improving ARSH value range tracking, the register representing
"max_len - usize" will have smin_value equal to S64_MIN and will be
rejected by verifier.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools/testing/selftests/bpf/bpf_helpers.h')
0 files changed, 0 insertions, 0 deletions