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Tue, 18 Aug 2026 04:44:14 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (smtpav06.fra02v.mail.ibm.com [10.20.54.105]) by smtprelay02.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 67I4i9gw51708378 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 18 Aug 2026 04:44:10 GMT Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D222C20040; Tue, 18 Aug 2026 04:44:09 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1A88720049; Tue, 18 Aug 2026 04:43:56 +0000 (GMT) Received: from li-1cb9f04c-2ae1-11b2-a85c-a8a0a83790a8.ibm.com.com (unknown [9.39.17.69]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 18 Aug 2026 04:43:55 +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 v12 1/8] powerpc/bpf: fix buffer overflow in JIT for large BPF programs Date: Tue, 18 Aug 2026 10:13:34 +0530 Message-ID: <191961a8100f3656a01ab826a02d43c765d02464.1787027080.git.skb99@linux.ibm.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=OfaoyBTY c=1 sm=1 tr=0 ts=6a83e31e cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=BWs5Yjlbf5yakj1inp4A:9 X-Proofpoint-Spam-Info: AW1haW4tMjYwODE4MDAzMSBTYWx0ZWRfX7zY8z8Doz2bZ oSWQRNyBE79t7/FX7ePtK+V8BJO0FNKKeeBF8Q0qqslE46lrDdRK8FOI/BFd4Pdht4Uys/KDEvC Hp5ZJd8BKc9O0EQAOEcKTgep7prah5w= X-Proofpoint-GUID: w83ieldg8ppkzja1qXNnVkUASfTJB5m3 X-Proofpoint-ORIG-GUID: w83ieldg8ppkzja1qXNnVkUASfTJB5m3 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE4MDAzMSBTYWx0ZWRfXwr+de8r1PRN6 wRPGz2ArjoV/De3vEDkw92QVUdD5xngSbQirp6iWzFZbnsn9UJUMSN3WGFtGzscFmebABP6kv3p FRQSNi7/L3Io52dJll4Q7vAtrYwtTjq9af353+vZycdNaZ4p/XHtHqI2zcDqjT7eSkv4FE8Ieow ZpJJn8WXf6f8Y+FVYj479/a5ijtUEwWHIO8sXqGW1opI0eiq9eLps8NXzs296kiY91p6lgs0Z0N QGDL/ZuSVIRapM3MeXA+oz3HRe5aqpbMarZruwZLCwhUb31hyCDcf/nXu27hGH7kHXf8z90rCob vGwu3+t16XYAl5wAGfW3VFwsfvfhAAEnN7outxi/4E99/4g5mqKSXLjLvXNgLuTQn61akhV/bhp ukxw7KpZvWH76pWcZrMoaS4uBuH0JQHvT7QmNCaX7ic/gfb+S9CWehC5IIv7lI9R0bVWydQpYez I8Nnfc0iuK0VMkdOodA== 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=2026-08-17_04,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 malwarescore=0 bulkscore=0 phishscore=0 priorityscore=1501 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608180031 From: Abhishek Dubey During size calculation in pass-0, exit_addr is 0 since addrs[fp->len] is not yet populated. bpf_jit_emit_exit_insn() treats a zero exit_addr as in-range and skips bpf_jit_build_epilogue(), so the alternate inline epilogue instructions are not counted in alloclen. In later passes, if the real exit_addr falls outside the 32MB branch range, the full inline epilogue is emitted into the already-allocated buffer, writing past its end and corrupting adjacent memory. Fix by ensuring exit_addr is non-zero before treating it as in-range, so pass-0 always falls through to bpf_jit_build_epilogue() and conservatively accounts for all epilogue instructions in alloclen. Also range check alt_exit_addr directly in the else-if condition. Since exit_addr handling now falls through to the epilogue, two related issues in bpf_int_jit_compile() must also be addressed: 1. Reset cgctx.alt_exit_addr before the second size-calculation pass. Without this, a stale alt_exit_addr from the first pass causes the second pass to emit a single jump instead of the full epilogue, undercounting alloclen and reintroducing the overflow. 2. Recompute addrs[fp->len] at the end of each code-generation pass. The larger pass-0 body can shrink in later passes as out-of-range exits settle into in-range jumps; a stale addrs[fp->len] would leave exit branches targeting past the real (shrunken) epilogue. Because shrinkage in a later pass can move the epilogue offset, the fixed two-pass loop is no longer sufficient: an exit that was out of range in an earlier pass may fall in range once the epilogue offset shrinks, shrinking the body further and overwriting the start of the epilogue. Convert the code-generation loop to iterate until the program size converges, bounded by CODEGEN_MAX_PASSES, and fail the JIT if it does not converge. Reported-by: sashiko-bot@kernel.org Closes: https://lore.kernel.org/bpf/20260529015855.364704-2-adubey@linux.ibm.com/T/#mfcb23909d977b949727cca4f59ee56a13fd69b92 Fixes: d243b62b7bd3 ("powerpc64/bpf: Add support for bpf trampolines") Cc: stable@vger.kernel.org Signed-off-by: Hari Bathini Signed-off-by: Abhishek Dubey Signed-off-by: Saket Kumar Bhaskar Link: https://lore.kernel.org/bpf/20260529015855.364704-2-adubey@linux.ibm.com/T/#mfcb23909d977b949727cca4f59ee56a13fd69b92 Tested-by: Yeswanth Krishna Tellakula --- arch/powerpc/net/bpf_jit.h | 7 +++++++ arch/powerpc/net/bpf_jit_comp.c | 34 +++++++++++++++++++++++++-------- 2 files changed, 33 insertions(+), 8 deletions(-) diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h index f32de8704d4d..995308654a56 100644 --- a/arch/powerpc/net/bpf_jit.h +++ b/arch/powerpc/net/bpf_jit.h @@ -14,6 +14,13 @@ #include #include +/* + * We need at least 2 passes for proper code generation, and may need + * additional passes if code size changes between passes. + */ +#define CODEGEN_MIN_PASSES 2 +#define CODEGEN_MAX_PASSES 3 + #ifdef CONFIG_PPC64_ELF_ABI_V1 #define FUNCTION_DESCR_SIZE 24 #else diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 7b07b43575f1..8bee2674d4a9 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -99,11 +99,10 @@ void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx) int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr) { - if (!exit_addr || is_offset_in_branch_range(exit_addr - (ctx->idx * 4))) { + if (exit_addr && is_offset_in_branch_range(exit_addr - (long)(ctx->idx * 4))) { PPC_JMP(exit_addr); - } else if (ctx->alt_exit_addr) { - if (WARN_ON(!is_offset_in_branch_range((long)ctx->alt_exit_addr - (ctx->idx * 4)))) - return -1; + } else if (ctx->alt_exit_addr && is_offset_in_branch_range( + (long)(ctx->alt_exit_addr) - (long)(ctx->idx * 4))) { PPC_JMP(ctx->alt_exit_addr); } else { ctx->alt_exit_addr = ctx->idx * 4; @@ -274,6 +273,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr */ if (cgctx.seen & SEEN_TAILCALL || !is_offset_in_branch_range((long)cgctx.idx * 4)) { cgctx.idx = 0; + cgctx.alt_exit_addr = 0; if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) goto out_err; } @@ -306,10 +306,13 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr code_base = (u32 *)(image + FUNCTION_DESCR_SIZE); fcode_base = (u32 *)(fimage + FUNCTION_DESCR_SIZE); - /* Code generation passes 1-2 */ - for (pass = 1; pass < 3; pass++) { + /* Code generation passes 1-2+, loop until program size converges. */ + for (pass = 1; pass <= CODEGEN_MAX_PASSES; pass++) { + u32 prev_proglen = proglen; + /* Now build the prologue, body code & epilogue for real. */ cgctx.idx = 0; + cgctx.exentry_idx = 0; cgctx.alt_exit_addr = 0; bpf_jit_build_prologue(code_base, &cgctx); if (bpf_jit_build_body(fp, code_base, fcode_base, &cgctx, addrs, pass, @@ -318,11 +321,26 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr bpf_jit_binary_pack_free(fhdr, hdr); goto out_err; } + addrs[fp->len] = cgctx.idx * 4; bpf_jit_build_epilogue(code_base, &cgctx); + proglen = cgctx.idx * 4; + if (bpf_jit_enable > 1) pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass, - proglen - (cgctx.idx * 4), cgctx.seen); + prev_proglen - proglen, cgctx.seen); + + /* Check if program size has converged, but ensure minimum passes */ + if (pass >= CODEGEN_MIN_PASSES && proglen == prev_proglen) + break; + + if (pass == CODEGEN_MAX_PASSES && proglen != prev_proglen) { + pr_err("BPF JIT: Program did not converge after %d passes\n", + CODEGEN_MAX_PASSES); + bpf_arch_text_copy(&fhdr->size, &hdr->size, sizeof(hdr->size)); + bpf_jit_binary_pack_free(fhdr, hdr); + goto out_err; + } } if (bpf_jit_enable > 1) @@ -399,7 +417,7 @@ int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, u32 *fimage, int pass u32 *fixup; /* Populate extable entries only in the last pass */ - if (pass != 2) + if (pass < CODEGEN_MIN_PASSES) return 0; if (!fp->aux->extable || -- 2.55.0