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b7a0d65d80
With latest llvm compiler, running test_progs will have the following verifier failure for test_sysctl_loop1.o: libbpf: load bpf program failed: Permission denied libbpf: -- BEGIN DUMP LOG --- libbpf: invalid indirect read from stack var_off (0x0; 0xff)+196 size 7 ... libbpf: -- END LOG -- libbpf: failed to load program 'cgroup/sysctl' libbpf: failed to load object 'test_sysctl_loop1.o' The related bytecode looks as below: 0000000000000308 LBB0_8: 97: r4 = r10 98: r4 += -288 99: r4 += r7 100: w8 &= 255 101: r1 = r10 102: r1 += -488 103: r1 += r8 104: r2 = 7 105: r3 = 0 106: call 106 107: w1 = w0 108: w1 += -1 109: if w1 > 6 goto -24 <LBB0_5> 110: w0 += w8 111: r7 += 8 112: w8 = w0 113: if r7 != 224 goto -17 <LBB0_8> And source code: for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) { ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, tcp_mem + i); if (ret <= 0 || ret > MAX_ULONG_STR_LEN) return 0; off += ret & MAX_ULONG_STR_LEN; } Current verifier is not able to conclude that register w0 before '+' at insn 110 has a range of 1 to 7 and thinks it is from 0 - 255. This leads to more conservative range for w8 at insn 112, and later verifier complaint. Let us workaround this issue until we found a compiler and/or verifier solution. The workaround in this patch is to make variable 'ret' volatile, which will force a reload and then '&' operation to ensure better value range. With this patch, I got the below byte code for the loop: 0000000000000328 LBB0_9: 101: r4 = r10 102: r4 += -288 103: r4 += r7 104: w8 &= 255 105: r1 = r10 106: r1 += -488 107: r1 += r8 108: r2 = 7 109: r3 = 0 110: call 106 111: *(u32 *)(r10 - 64) = r0 112: r1 = *(u32 *)(r10 - 64) 113: if w1 s< 1 goto -28 <LBB0_5> 114: r1 = *(u32 *)(r10 - 64) 115: if w1 s> 7 goto -30 <LBB0_5> 116: r1 = *(u32 *)(r10 - 64) 117: w1 &= 7 118: w1 += w8 119: r7 += 8 120: w8 = w1 121: if r7 != 224 goto -21 <LBB0_9> Insn 117 did the '&' operation and we got more precise value range for 'w8' at insn 120. The test is happy then: #3/17 test_sysctl_loop1.o:OK Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20191107170045.2503480-1-yhs@fb.com |
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.. | ||
accounting | ||
arch | ||
bpf | ||
build | ||
cgroup | ||
debugging | ||
firewire | ||
firmware | ||
gpio | ||
hv | ||
iio | ||
include | ||
io_uring | ||
kvm/kvm_stat | ||
laptop | ||
leds | ||
lib | ||
memory-model | ||
nfsd | ||
objtool | ||
pci | ||
pcmcia | ||
perf | ||
power | ||
scripts | ||
spi | ||
testing | ||
thermal/tmon | ||
time | ||
usb | ||
virtio | ||
vm | ||
wmi | ||
Makefile |