96752e1ec0
With latest llvm15, test_varlen failed with the following verifier log:
17: (85) call bpf_probe_read_kernel_str#115 ; R0_w=scalar(smin=-4095,smax=256)
18: (bf) r1 = r0 ; R0_w=scalar(id=1,smin=-4095,smax=256) R1_w=scalar(id=1,smin=-4095,smax=256)
19: (67) r1 <<= 32 ; R1_w=scalar(smax=1099511627776,umax=18446744069414584320,var_off=(0x0; 0xffffffff00000000),s32_min=0,s32_max=0,u32_max=)
20: (bf) r2 = r1 ; R1_w=scalar(id=2,smax=1099511627776,umax=18446744069414584320,var_off=(0x0; 0xffffffff00000000),s32_min=0,s32_max=0,u32)
21: (c7) r2 s>>= 32 ; R2=scalar(smin=-2147483648,smax=256)
; if (len >= 0) {
22: (c5) if r2 s< 0x0 goto pc+7 ; R2=scalar(umax=256,var_off=(0x0; 0x1ff))
; payload4_len1 = len;
23: (18) r2 = 0xffffc90000167418 ; R2_w=map_value(off=1048,ks=4,vs=1572,imm=0)
25: (63) *(u32 *)(r2 +0) = r0 ; R0=scalar(id=1,smin=-4095,smax=256) R2_w=map_value(off=1048,ks=4,vs=1572,imm=0)
26: (77) r1 >>= 32 ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; payload += len;
27: (18) r6 = 0xffffc90000167424 ; R6_w=map_value(off=1060,ks=4,vs=1572,imm=0)
29: (0f) r6 += r1 ; R1_w=Pscalar(umax=4294967295,var_off=(0x0; 0xffffffff)) R6_w=map_value(off=1060,ks=4,vs=1572,umax=4294967295,var_off=(0)
; len = bpf_probe_read_kernel_str(payload, MAX_LEN, &buf_in2[0]);
30: (bf) r1 = r6 ; R1_w=map_value(off=1060,ks=4,vs=1572,umax=4294967295,var_off=(0x0; 0xffffffff)) R6_w=map_value(off=1060,ks=4,vs=1572,um)
31: (b7) r2 = 256 ; R2_w=256
32: (18) r3 = 0xffffc90000164100 ; R3_w=map_value(off=256,ks=4,vs=1056,imm=0)
34: (85) call bpf_probe_read_kernel_str#115
R1 unbounded memory access, make sure to bounds check any such access
processed 27 insns (limit 1000000) max_states_per_insn 0 total_states 2 peak_states 2 mark_read 1
-- END PROG LOAD LOG --
libbpf: failed to load program 'handler32_signed'
The failure is due to
20: (bf) r2 = r1 ; R1_w=scalar(id=2,smax=1099511627776,umax=18446744069414584320,var_off=(0x0; 0xffffffff00000000),s32_min=0,s32_max=0,u32)
21: (c7) r2 s>>= 32 ; R2=scalar(smin=-2147483648,smax=256)
22: (c5) if r2 s< 0x0 goto pc+7 ; R2=scalar(umax=256,var_off=(0x0; 0x1ff))
26: (77) r1 >>= 32 ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
29: (0f) r6 += r1 ; R1_w=Pscalar(umax=4294967295,var_off=(0x0; 0xffffffff)) R6_w=map_value(off=1060,ks=4,vs=1572,umax=4294967295,var_off=(0)
where r1 has conservative value range compared to r2 and r1 is used later.
In llvm, commit [1] triggered the above code generation and caused
verification failure.
It may take a while for llvm to address this issue. In the main time,
let us change the variable 'len' type to 'long' and adjust condition properly.
Tested with llvm14 and latest llvm15, both worked fine.
[1] https://reviews.llvm.org/D126647
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220613233449.2860753-1-yhs@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.