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Mon, 28 Sep 2026 05:13:55 +0000 (GMT) Received: from li-1cb9f04c-2ae1-11b2-a85c-a8a0a83790a8.ibm.com.com (unknown [9.124.213.52]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 28 Sep 2026 05:13:55 +0000 (GMT) From: Saket Kumar Bhaskar To: bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: hbathini@linux.ibm.com, maddy@linux.ibm.com, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, shuah@kernel.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org, venkat88@linux.ibm.com, yeswanth@linux.ibm.com, skb99@linux.ibm.com Subject: [PATCH v14 0/5] powerpc/bpf: address missing verifier selftest coverage Date: Mon, 28 Sep 2026 10:43:49 +0530 Message-ID: X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTI4MDAyMCBTYWx0ZWRfX7WeI6CftQTu8 M5anJd7OKEgtY7gmkk8T3nhGFh3F0Fi7yj6/oUvt0b0ztMmxVUTbJaBqPPDmCHbLcN8jR5zRlTY MO/zE9hPcTgpKnQ6M6afcDObj7KmfRA1IT/XRfeASqmqgrYDBVKRhq4j5KOK7I9Y/cL4+bLMxT+ qYS+nHCXmdAqSBSFj47o+odbFLaG7gTFWb7zDvUI3CC989K5nrQp04TWcEKFIArkbGyySwwWjJJ /w2/JbvDYHuqw/hPubL6xUxsmxikZYY5qg2N7rpenZb+Uh0Codb1FRWODrVfhStqsBh0dhlcNIT gOld2tAJMmfphqv+iqyZKGDmOGMiO5TwGJ0FLtoWk/be1dvzogrjJMNJ2omPqpJ1+gMzNdOWCbs lO0FSO04fJKoUVdTHVvVQY+z0MRiFupwqM7vDZQq933lAi80zee4mGyUMXRfNkTJ1U/oWUsBP70 gYjxvLFGzlDymi+XOZA== X-Authority-Analysis: v=2.4 cv=SPbXx+vH c=1 sm=1 tr=0 ts=6ab9f79c cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=N7QzuYTHEryR9oxcy7gA:9 X-Proofpoint-ORIG-GUID: MAT2wFh32BMloxLSoyCt5fstIMWucV84 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI4MDAyMCBTYWx0ZWRfX7pZirgXrEvxN Bmc02MXNlvwQUG3ZyHqg/Kl3A/jDVboVmBMBiab9IAyYGBrd1oI9/EN/ychnNbq6HbWApRVAfCO 7HpHOXXd+elyXgXZgWthVQmEpXmsReE= X-Proofpoint-GUID: MAT2wFh32BMloxLSoyCt5fstIMWucV84 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-26_05,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 clxscore=1015 spamscore=0 lowpriorityscore=0 malwarescore=0 adultscore=0 bulkscore=0 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609280020 From: Abhishek Dubey The verifier selftest validates JITed instructions by matching expected disassembly output. The first two patches fix issues in powerpc instruction disassembly that were causing test flow failures. The fix is common for 64-bit & 32-bit powerpc. Add support for the powerpc-specific "__powerpc64" architecture tag in the third patch, enabling proper test filtering in verifier test files. Introduce verifier testcases for tailcalls on powerpc64. The first patch in series is fix patch, correcting memory alignment with 8-byte boundary for long branch address field. The subsequent patches enables verifier selftests on powerpc. The fifth patch in the series fixes incorrect comparator usage for comparing tailcall info with tailcall threshold. The last two patches fix JIT buffer overflow for large BPF progs and private stack memory leak (identified by bot during reviews). Issue Details: -------------- The Long branch stub in the trampoline implementation[1] provides flexibility to handles short as well as long branch distance to actual trampoline. Whereas, the 8 bytes long dummy_tramp_addr field sitting before long branch stub leads to failure when enabling verifier based seltest for ppc64. The verifier selftests require disassembing the final jited image to get native instructions. Later the disassembled instruction sequence is matched against sequence of instructions provided in test-file under __jited() wrapper. The final jited image contains Out-of-line stub and Long branch stub as part of epilogue jitting for a bpf program. The 8 bytes space for dummy_tramp is sandwiched between both above mentioned stubs. These 8 bytes contain memory address of dummy trampoline during trampoline invocation which don't correspond to any powerpc instructions. So, disassembly fails resulting in failure of verifier selftests. The following code snippet shows the problem with current arrangement made for dummy_tramp_addr. /* Out-of-line stub */ mflr r0 [b|bl] tramp mtlr r0 //only with OOL b bpf_func + 4 /* Long branch stub */ .long <---Invalid bytes sequence, disassembly fails mflr r11 bcl 20,31,$+4 mflr r12 ld r12, -8-SZL(r12) mtctr r12 mtlr r11 //retain ftrace ABI bctr Consider test program binary of size 112 bytes: 0: 00000060 10004de8 00002039 f8ff21f9 81ff21f8 7000e1fb 3000e13b 28: 3000e13b 2a006038 f8ff7ff8 00000039 7000e1eb 80002138 7843037d 56: 2000804e a602087c 00000060 a603087c bcffff4b c0341d00 000000c0 84: a602687d 05009f42 a602887d f0ff8ce9 a603897d a603687d 2004804e Disassembly output of above binary for ppc64le: pc:0 left:112 00 00 00 60 : nop pc:4 left:108 10 00 4d e8 : ld 2, 16(13) pc:8 left:104 00 00 20 39 : li 9, 0 pc:12 left:100 f8 ff 21 f9 : std 9, -8(1) pc:16 left:96 81 ff 21 f8 : stdu 1, -128(1) pc:20 left:92 70 00 e1 fb : std 31, 112(1) pc:24 left:88 30 00 e1 3b : addi 31, 1, 48 pc:28 left:84 30 00 e1 3b : addi 31, 1, 48 pc:32 left:80 2a 00 60 38 : li 3, 42 pc:36 left:76 f8 ff 7f f8 : std 3, -8(31) pc:40 left:72 00 00 00 39 : li 8, 0 pc:44 left:68 70 00 e1 eb : ld 31, 112(1) pc:48 left:64 80 00 21 38 : addi 1, 1, 128 pc:52 left:60 78 43 03 7d : mr 3, 8 pc:56 left:56 20 00 80 4e : blr pc:60 left:52 a6 02 08 7c : mflr 0 pc:64 left:48 00 00 00 60 : nop pc:68 left:44 a6 03 08 7c : mtlr 0 pc:72 left:40 bc ff ff 4b : b .-68 pc:76 left:36 c0 34 1d 00 : ... Failure log: Can't disasm instruction at offset 76: c0 34 1d 00 00 00 00 c0 a6 02 68 7d 05 00 9f 42 -------------------------------------- Observation: Can't disasm instruction at offset 76 as this address has ".long " (0xc0341d00000000c0) But valid instructions follow at offset 84 onwards. Move the long branch address space to the bottom of the long branch stub. This allows uninterrupted disassembly until the last 8 bytes. Exclude these last bytes from the overall program length to prevent failure in assembly generation. Following is disassembler output for same test program with moved down dummy_tramp_addr field: ..... ..... pc:68 left:44 a6 03 08 7c : mtlr 0 pc:72 left:40 bc ff ff 4b : b .-68 pc:76 left:36 a6 02 68 7d : mflr 11 pc:80 left:32 05 00 9f 42 : bcl 20, 31, .+4 pc:84 left:28 a6 02 88 7d : mflr 12 pc:88 left:24 14 00 8c e9 : ld 12, 20(12) pc:92 left:20 a6 03 89 7d : mtctr 12 pc:96 left:16 a6 03 68 7d : mtlr 11 pc:100 left:12 20 04 80 4e : bctr pc:104 left:8 c0 34 1d 00 : Failure log: Can't disasm instruction at offset 104: c0 34 1d 00 00 00 00 c0 --------------------------------------- Disassembly logic can truncate at 104, ignoring last 8 bytes. Update the dummy_tramp_addr field offset calculation from the end of the program to reflect its new location, for bpf_arch_text_poke() to update the actual trampoline's address in this field. [1] https://lore.kernel.org/all/20241030070850.1361304-18-hbathini@linux.ibm.com v13->v14: Corrected Fixes: tag for 3/8. Decoupled selftest patches, to be send separately as follow up with all the fixes suggested by sashiko and bpf-bot. All pre-existing issues flagged by sashiko and bpf-bot will also be handled in separate set of patches. v12->v13: Moved patch 4 and 5 before 1. Modified comments in code. v11->v12: Fix build failure for ppc32 Rearranged the order of patches as suggested by Hari v10->v11: Moved function prototype change from patch 2 to patch 1 Fixed commit message for patch 1 and patch 4 Fixed extable entry generation condition Added reviewed and acked tags by Hari v9->v10: Modified expected JIT instruction in selftest for CONFIG_PPC_KERNEL_PCREL incase of PPC_LI64 instruction. Fix for stale entries in exception table Update ARCH_POWERPC64 enum value to 0x40 to resolve rebase conflict with ARCH_LOONGARCH (0x20). v8->v9: Dynamic pass handling until code keeps shrinking Fix private stack memory leak v7->v8: Fixed bot identified issues of alt_exit_addr and BPF_EXIT Fixed 32-bit ppc function signature mismatch v6->v7: Fixed JIT buffer overflow in case of large BPF progs Addressed remaining bot comments v5->v6: Changed alignment NOP emittion dependency on fimage layout Adjust tail truncate length for 32-bit ppc Addressed few minor bot comments v4->v5: Handled alignment NOP emit logic and corresponding stub offsets Handled image buffer overflow problem in last pass Above changes took care of other bot reviews Included LLVMDisposeMessage() for graceful freeing Adjusted parameters in bpf_jit_build_fentry_stubs for ppc32 Adjusted expected JIT inst. in tailcall test for CONFIG_PPC_KERNEL_PCREL config Added fix patch at last for inaccurate use of cmplwi inst. v3->v4: Changed logic for emitting alignment NOP v2->v3: Removed fixed NOP from bottom of long branch stub Rebased on top of bpf-next v1->v2: Added fix-patch to correct memory alignment in-place Moved the optional alignmnet NOP before OOL stub [v1]: https://lore.kernel.org/bpf/20260225013627.22098-1-adubey@linux.ibm.com [v2]: https://lore.kernel.org/bpf/20260403004011.44417-1-adubey@linux.ibm.com [v3]: https://lore.kernel.org/bpf/20260411221413.44304-1-adubey@linux.ibm.com [v4]: https://lore.kernel.org/bpf/20260517214043.12975-1-adubey@linux.ibm.com [v5]: https://lore.kernel.org/bpf/20260519233812.18787-1-adubey@linux.ibm.com [v6]: https://lore.kernel.org/bpf/20260529015855.364704-1-adubey@linux.ibm.com [v7]: https://lore.kernel.org/bpf/20260611153826.31187-1-adubey@linux.ibm.com [v8]: https://lore.kernel.org/bpf/20260616164741.32252-1-adubey@linux.ibm.com [v9]: https://lore.kernel.org/bpf/20260623231411.6216-1-adubey@linux.ibm.com/ [v10]: https://lore.kernel.org/all/cover.1785871099.git.skb99@linux.ibm.com/ [v11]: https://lore.kernel.org/all/cover.1785871099.git.skb99@linux.ibm.com/#r [v12]: https://lore.kernel.org/all/cover.1786611077.git.skb99@linux.ibm.com/ [v13]: https://lore.kernel.org/all/cover.1788154635.git.skb99@linux.ibm.com/ Abhishek Dubey (5): powerpc64/bpf: fix compare instruction emitted for tailcall powerpc64/bpf: fix percpu private stack leak on JIT failure powerpc/bpf: fix buffer overflow in JIT for large BPF programs powerpc/bpf: fix alignment of long branch trampoline address powerpc/bpf: Move out dummy_tramp_addr after Long branch stub arch/powerpc/net/bpf_jit.h | 20 +++++- arch/powerpc/net/bpf_jit_comp.c | 100 ++++++++++++++++++++++-------- arch/powerpc/net/bpf_jit_comp32.c | 7 ++- arch/powerpc/net/bpf_jit_comp64.c | 15 ++--- 4 files changed, 103 insertions(+), 39 deletions(-) -- 2.55.0