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Mon, 31 Aug 2026 07:16:26 +0000 (GMT) Received: from li-1cb9f04c-2ae1-11b2-a85c-a8a0a83790a8.ibm.com.com (unknown [9.67.146.121]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 31 Aug 2026 07:16:26 +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 v13 3/8] powerpc/bpf: fix buffer overflow in JIT for large BPF programs Date: Mon, 31 Aug 2026 12:46:00 +0530 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kselftest@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: AW1haW4tMjYwODMxMDA1OSBTYWx0ZWRfX2SaUJitDB+Fc TMRMO0swnH6EHGqCnFDJ1HrUFfpVD9VB+LyTTDAxdXKrVDW0ABg+/rauubkAKOcg3Ly53Bdm20D XNKwvrx0ELM4L9tAXm3xHXkasTycpNO2AoxulsTzV1RpOThFsmGJB7Knd1IptMtacEWZozPwpDd fBaLmoBlzHQinU6gI1KY5MmsBlKoURe5jdiRD9oEQKmY7BIt6bsyIySyMhZX8dMjvm2WyUoJ1Iu FU56QA6Cto3eX41SxoBVbuaCO1zHpncMSx8KxArVBPpZlbWvPRxxAC8K2KoWqHCYUcThCs9s1LQ Pa46WD1Eqlyvzijq9HRwEJdepvHu2YUDuBEKtM+hWeO4whFbeVECPgs3y8cN+YJgLIBQBxUEAj1 +ZB7649FsfoI+UTkINxAOHxF/HmH0t5xBNx0IOH8Yc7dil5z+PdwWLS43b+d6xkSvJH0GWqXwUH o2YJvcYSy1w1Xj0r0Sg== X-Proofpoint-ORIG-GUID: JcyE7rUqBIVL_1fMufxjmAuPKPi3PQUl X-Authority-Analysis: v=2.4 cv=CNgamxrD c=1 sm=1 tr=0 ts=6a952a57 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=BWs5Yjlbf5yakj1inp4A:9 X-Proofpoint-GUID: JcyE7rUqBIVL_1fMufxjmAuPKPi3PQUl X-Proofpoint-Spam-Info: AW1haW4tMjYwODMxMDA1OSBTYWx0ZWRfX67mrNW61Q3E2 tu/UJkBUSFOAzMyIzAONvofCeZbNv4LxxKZ1rwGQKCiD+Z+bn6Cg1Cf1Oouv+nznsv8B0+HgoT2 5T8kob2Ah2CbA/s6/DqFSicXcKp34dw= 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=2026-08-31_02,2026-08-27_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 suspectscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1015 impostorscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608310059 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 35015d7ecb76..6d58df361648 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 8f7501954d9f..11981d2270a9 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