On Mon, Sep 14, 2020 at 01:20:43PM +0100, Will Deacon wrote: > On Mon, Sep 14, 2020 at 11:36:21AM +0300, Ilias Apalodimas wrote: > > Running the eBPF test_verifier leads to random errors looking like this: > > > > [ 6525.735488] Unexpected kernel BRK exception at EL1 > > [ 6525.735502] Internal error: ptrace BRK handler: f2000100 [#1] SMP > > [ 6525.741609] Modules linked in: nls_utf8 cifs libdes libarc4 dns_resolver fscache binfmt_misc nls_ascii nls_cp437 vfat fat aes_ce_blk crypto_simd cryptd aes_ce_cipher ghash_ce gf128mul efi_pstore sha2_ce sha256_arm64 sha1_ce evdev efivars efivarfs ip_tables x_tables autofs4 btrfs blake2b_generic xor xor_neon zstd_compress raid6_pq libcrc32c crc32c_generic ahci xhci_pci libahci xhci_hcd igb libata i2c_algo_bit nvme realtek usbcore nvme_core scsi_mod t10_pi netsec mdio_devres of_mdio gpio_keys fixed_phy libphy gpio_mb86s7x > > [ 6525.787760] CPU: 3 PID: 7881 Comm: test_verifier Tainted: G W 5.9.0-rc1+ #47 > > [ 6525.796111] Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #1 Jun 6 2020 > > [ 6525.804812] pstate: 20000005 (nzCv daif -PAN -UAO BTYPE=--) > > [ 6525.810390] pc : bpf_prog_c3d01833289b6311_F+0xc8/0x9f4 > > [ 6525.815613] lr : bpf_prog_d53bb52e3f4483f9_F+0x38/0xc8c > > [ 6525.820832] sp : ffff8000130cbb80 > > [ 6525.824141] x29: ffff8000130cbbb0 x28: 0000000000000000 > > [ 6525.829451] x27: 000005ef6fcbf39b x26: 0000000000000000 > > [ 6525.834759] x25: ffff8000130cbb80 x24: ffff800011dc7038 > > [ 6525.840067] x23: ffff8000130cbd00 x22: ffff0008f624d080 > > [ 6525.845375] x21: 0000000000000001 x20: ffff800011dc7000 > > [ 6525.850682] x19: 0000000000000000 x18: 0000000000000000 > > [ 6525.855990] x17: 0000000000000000 x16: 0000000000000000 > > [ 6525.861298] x15: 0000000000000000 x14: 0000000000000000 > > [ 6525.866606] x13: 0000000000000000 x12: 0000000000000000 > > [ 6525.871913] x11: 0000000000000001 x10: ffff8000000a660c > > [ 6525.877220] x9 : ffff800010951810 x8 : ffff8000130cbc38 > > [ 6525.882528] x7 : 0000000000000000 x6 : 0000009864cfa881 > > [ 6525.887836] x5 : 00ffffffffffffff x4 : 002880ba1a0b3e9f > > [ 6525.893144] x3 : 0000000000000018 x2 : ffff8000000a4374 > > [ 6525.898452] x1 : 000000000000000a x0 : 0000000000000009 > > [ 6525.903760] Call trace: > > [ 6525.906202] bpf_prog_c3d01833289b6311_F+0xc8/0x9f4 > > [ 6525.911076] bpf_prog_d53bb52e3f4483f9_F+0x38/0xc8c > > [ 6525.915957] bpf_dispatcher_xdp_func+0x14/0x20 > > [ 6525.920398] bpf_test_run+0x70/0x1b0 > > [ 6525.923969] bpf_prog_test_run_xdp+0xec/0x190 > > [ 6525.928326] __do_sys_bpf+0xc88/0x1b28 > > [ 6525.932072] __arm64_sys_bpf+0x24/0x30 > > [ 6525.935820] el0_svc_common.constprop.0+0x70/0x168 > > [ 6525.940607] do_el0_svc+0x28/0x88 > > [ 6525.943920] el0_sync_handler+0x88/0x190 > > [ 6525.947838] el0_sync+0x140/0x180 > > [ 6525.951154] Code: d4202000 d4202000 d4202000 d4202000 (d4202000) > > [ 6525.957249] ---[ end trace cecc3f93b14927e2 ]--- > > > > The reason seems to be the offset[] creation and usage ctx->offset[] > > "seems to be"? Are you unsure? Reading the history and other ports of the JIT implementation, I couldn't tell if the decision on skipping the 1st entry was deliberate or not on Aarch64. Reading through the mailist list didn't help either [1]. Skipping the 1st entry seems indeed to cause the problem. I did run the patch though the BPF tests and showed no regressions + fixing the error. > > > while building the eBPF body. The code currently omits the first > > instruction, since build_insn() will increase our ctx->idx before saving > > it. When "taken loop with back jump to 1st insn" test runs it will > > eventually call bpf2a64_offset(-1, 2, ctx). Since negative indexing is > > permitted, the current outcome depends on the value stored in > > ctx->offset[-1], which has nothing to do with our array. > > If the value happens to be 0 the tests will work. If not this error > > triggers. > > > > So let's fix it by creating the ctx->offset[] correctly in the first > > place and account for the extra instruction while calculating the arm > > instruction offsets. > > No Fixes: tag? I'll re-spin and apply one > > > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> > > Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@xxxxxxxxxx> > > Non-author signoffs here. What's going on? My bad here, I'll add a Co-developed-by on v2 for the rest of the people and move my Signed-off last [1] https://lore.kernel.org/bpf/CANoWswkaj1HysW3BxBMG9_nd48fm0MxM5egdtmHU6YsEc_GUtQ@xxxxxxxxxxxxxx/T/#u Thanks /Ilias > > Will
