Messages in this thread | | | Date | Thu, 24 Nov 2022 15:56:15 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH v2] powerpc/bpf/32: Fix Oops on tail call tests |
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Christophe Leroy wrote: > test_bpf tail call tests end up as: > > test_bpf: #0 Tail call leaf jited:1 85 PASS > test_bpf: #1 Tail call 2 jited:1 111 PASS > test_bpf: #2 Tail call 3 jited:1 145 PASS > test_bpf: #3 Tail call 4 jited:1 170 PASS > test_bpf: #4 Tail call load/store leaf jited:1 190 PASS > test_bpf: #5 Tail call load/store jited:1 > BUG: Unable to handle kernel data access on write at 0xf1b4e000 > Faulting instruction address: 0xbe86b710 > Oops: Kernel access of bad area, sig: 11 [#1] > BE PAGE_SIZE=4K MMU=Hash PowerMac > Modules linked in: test_bpf(+) > CPU: 0 PID: 97 Comm: insmod Not tainted 6.1.0-rc4+ #195 > Hardware name: PowerMac3,1 750CL 0x87210 PowerMac > NIP: be86b710 LR: be857e88 CTR: be86b704 > REGS: f1b4df20 TRAP: 0300 Not tainted (6.1.0-rc4+) > MSR: 00009032 <EE,ME,IR,DR,RI> CR: 28008242 XER: 00000000 > DAR: f1b4e000 DSISR: 42000000 > GPR00: 00000001 f1b4dfe0 c11d2280 00000000 00000000 00000000 00000002 00000000 > GPR08: f1b4e000 be86b704 f1b4e000 00000000 00000000 100d816a f2440000 fe73baa8 > GPR16: f2458000 00000000 c1941ae4 f1fe2248 00000045 c0de0000 f2458030 00000000 > GPR24: 000003e8 0000000f f2458000 f1b4dc90 3e584b46 00000000 f24466a0 c1941a00 > NIP [be86b710] 0xbe86b710 > LR [be857e88] __run_one+0xec/0x264 [test_bpf] > Call Trace: > [f1b4dfe0] [00000002] 0x2 (unreliable) > Instruction dump: > XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX > XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX > ---[ end trace 0000000000000000 ]--- > > This is a tentative to write above the stack. The problem is encoutered > with tests added by commit 38608ee7b690 ("bpf, tests: Add load store > test case for tail call") > > This happens because tail call is done to a BPF prog with a different > stack_depth. At the time being, the stack is kept as is when the caller > tail calls its callee. But at exit, the callee restores the stack based > on its own properties. Therefore here, at each run, r1 is erroneously > increased by 32 - 16 = 16 bytes. > > This was done that way in order to pass the tail call count from caller > to callee through the stack. As powerpc32 doesn't have a red zone in > the stack, it was necessary the maintain the stack as is for the tail > call. But it was not anticipated that the BPF frame size could be > different. > > Let's take a new approach. Use register r4 to carry the tail call count > during the tail call, and save it into the stack at function entry if > required. This means the input parameter must be in r3, which is more > correct as it is a 32 bits parameter, then tail call better match with > normal BPF function entry, the down side being that we move that input > parameter back and forth between r3 and r4. That can be optimised later. > > Doing that also has the advantage of maximising the common parts between > tail calls and a normal function exit. > > With the fix, tail call tests are now successfull: > > test_bpf: #0 Tail call leaf jited:1 53 PASS > test_bpf: #1 Tail call 2 jited:1 115 PASS > test_bpf: #2 Tail call 3 jited:1 154 PASS > test_bpf: #3 Tail call 4 jited:1 165 PASS > test_bpf: #4 Tail call load/store leaf jited:1 101 PASS > test_bpf: #5 Tail call load/store jited:1 141 PASS > test_bpf: #6 Tail call error path, max count reached jited:1 994 PASS > test_bpf: #7 Tail call count preserved across function calls jited:1 140975 PASS > test_bpf: #8 Tail call error path, NULL target jited:1 110 PASS > test_bpf: #9 Tail call error path, index out of range jited:1 69 PASS > test_bpf: test_tail_calls: Summary: 10 PASSED, 0 FAILED, [10/10 JIT'ed] > > Suggested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> > Fixes: 51c66ad849a7 ("powerpc/bpf: Implement extended BPF on PPC32") > Cc: stable@vger.kernel.org > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com
Thanks, Naveen
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