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Wed, 25 Feb 2026 10:39:41 +0000 Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 61PAdbYx46727542 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 25 Feb 2026 10:39:37 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A51662004D; Wed, 25 Feb 2026 10:39:37 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 23CB420043; Wed, 25 Feb 2026 10:39:36 +0000 (GMT) Received: from ltcrain4-lp15.ltc.tadn.ibm.com (unknown [9.5.7.39]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 25 Feb 2026 10:39:35 +0000 (GMT) From: adubey@linux.ibm.com To: linuxppc-dev@lists.ozlabs.org Cc: bpf@vger.kernel.org, hbathini@linux.ibm.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, maddy@linux.ibm.com, Abhishek Dubey Subject: [PATCH v2 1/2] powerpc64/bpf: Implement JIT support for private stack Date: Wed, 25 Feb 2026 10:39:49 -0500 Message-ID: <20260225153950.15331-1-adubey@linux.ibm.com> X-Mailer: git-send-email 2.52.0 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-Proofpoint-ORIG-GUID: MBhtfZT89ulX7mU-dG2GURG9CGi_RgYR X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI1MDEwNCBTYWx0ZWRfX8e0X2UbPw/0o RE1LaAEo0djzLAU0h3si+uwb/CSqXSu4aw1zF6qgnHAFzFRyRCVz8H2sxXVoYwonIZP7RF1ijeV uyo8tXPD9dkjWVjqSNTTKxAaiEdy9YNNBJrrAhFgmsuX21LLVZEu1/p76CBlSCA8f+RW8kOacdl D+pmdKa1kk8NCJFO7QnVksmF46cBGfoCiidnU8Mf4J1/1MEoZW0tAMe8QzQ3mBNR7VK2O+NDenN 3T9na1mCONcdMeRYiOOPYxjlI4r+YUHsQm7OM0BDrH6w+wcIx06oyNjDAjKtLaejgG7cJZZJX11 3Bh++7Us8L8/FrO5wdIFzxiB96R3agyx8yqWq+Je2mNNg6fwkKtbt4WhW00mOeW4RlmaTSOKZn/ UlR6M/9cFFXiB2QG1ngbGZXIVFtCqgrd6pKeAQDMjineGuggaVuKFLtv4a6USxevY8i6ThWMNBu YVpsyNmTyrZxbFgh9Uw== X-Authority-Analysis: v=2.4 cv=R7wO2NRX c=1 sm=1 tr=0 ts=699ed16e cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=F76KSA7jxJ0ultxYvGsA:9 X-Proofpoint-GUID: MBhtfZT89ulX7mU-dG2GURG9CGi_RgYR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-24_03,2026-02-23_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 clxscore=1015 impostorscore=0 phishscore=0 spamscore=0 suspectscore=0 malwarescore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602250104 From: Abhishek Dubey Provision the private stack as a per-CPU allocation during bpf_int_jit_compile(). Align the stack to 16 bytes and place guard regions at both ends to detect runtime stack overflow and underflow. Round the private stack size up to the nearest 16-byte boundary. Make each guard region 16 bytes to preserve the required overall 16-byte alignment. When private stack is set, skip bpf stack size accounting in kernel stack. There is no stack pointer in powerpc. Stack referencing during JIT is done using frame pointer. Frame pointer calculation goes like: BPF frame pointer = Priv stack allocation start address + Overflow guard + Actual stack size defined by verifier Memory layout: High Addr +--------------------------------------------------+ | | | 16 bytes Underflow guard (0xEB9F12345678eb9fULL) | | | BPF FP -> +--------------------------------------------------+ | | | Private stack - determined by verifier | | 16-bytes aligned | | | +--------------------------------------------------+ | | Lower Addr | 16 byte Overflow guard (0xEB9F12345678eb9fULL) | | | Priv stack alloc ->+--------------------------------------------------+ start Update BPF_REG_FP to point to the calculated offset within the allocated private stack buffer. Now, BPF stack usage reference in the allocated private stack. The patch is rebase over fixes by Hari: https://lore.kernel.org/bpf/20260220063933.196141-1-hbathini@linux.ibm.com/ v1->v2: Fix ci-bot warning for percpu pointer casting Minor refactoring [v1]: https://lore.kernel.org/bpf/20260216152234.36632-1-adubey@linux.ibm.com Signed-off-by: Abhishek Dubey --- arch/powerpc/net/bpf_jit.h | 5 +++ arch/powerpc/net/bpf_jit_comp.c | 75 +++++++++++++++++++++++++++++++ arch/powerpc/net/bpf_jit_comp64.c | 34 +++++++++++--- 3 files changed, 109 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h index 7354e1d72f79..eb0a400b5a98 100644 --- a/arch/powerpc/net/bpf_jit.h +++ b/arch/powerpc/net/bpf_jit.h @@ -178,8 +178,13 @@ struct codegen_context { bool is_subprog; bool exception_boundary; bool exception_cb; + void __percpu *priv_sp; }; +/* Memory size & magic-value to detect private stack overflow/underflow */ +#define PRIV_STACK_GUARD_SZ 16 +#define PRIV_STACK_GUARD_VAL 0xEB9F12345678eb9fULL + #define bpf_to_ppc(r) (ctx->b2p[r]) #ifdef CONFIG_PPC32 diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 278e09b57560..ebd21c75ce47 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -129,6 +129,39 @@ bool bpf_jit_needs_zext(void) return true; } +static void priv_stack_init_guard(void __percpu *priv_stack_ptr, int alloc_size) +{ + int cpu, underflow_idx = (alloc_size - PRIV_STACK_GUARD_SZ) >> 3; + u64 *stack_ptr; + + for_each_possible_cpu(cpu) { + stack_ptr = per_cpu_ptr(priv_stack_ptr, cpu); + stack_ptr[0] = PRIV_STACK_GUARD_VAL; + stack_ptr[1] = PRIV_STACK_GUARD_VAL; + stack_ptr[underflow_idx] = PRIV_STACK_GUARD_VAL; + stack_ptr[underflow_idx + 1] = PRIV_STACK_GUARD_VAL; + } +} + +static void priv_stack_check_guard(void __percpu *priv_stack_ptr, int alloc_size, + struct bpf_prog *fp) +{ + int cpu, underflow_idx = (alloc_size - PRIV_STACK_GUARD_SZ) >> 3; + u64 *stack_ptr; + + for_each_possible_cpu(cpu) { + stack_ptr = per_cpu_ptr(priv_stack_ptr, cpu); + if (stack_ptr[0] != PRIV_STACK_GUARD_VAL || + stack_ptr[1] != PRIV_STACK_GUARD_VAL || + stack_ptr[underflow_idx] != PRIV_STACK_GUARD_VAL || + stack_ptr[underflow_idx + 1] != PRIV_STACK_GUARD_VAL) { + pr_err("BPF private stack overflow/underflow detected for prog %sx\n", + bpf_jit_get_prog_name(fp)); + break; + } + } +} + struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) { u32 proglen; @@ -140,6 +173,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) struct codegen_context cgctx; int pass; int flen; + int priv_stack_alloc_size; + void __percpu *priv_stack_ptr = NULL; struct bpf_binary_header *fhdr = NULL; struct bpf_binary_header *hdr = NULL; struct bpf_prog *org_fp = fp; @@ -173,6 +208,26 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) fp->aux->jit_data = jit_data; } + priv_stack_ptr = fp->aux->priv_stack_ptr; + if (!priv_stack_ptr && fp->aux->jits_use_priv_stack) { + /* + * Allocate private stack of size equivalent to + * verifier-calculated stack size plus two memory + * guard regions to detect private stack overflow + * and underflow. + */ + priv_stack_alloc_size = round_up(fp->aux->stack_depth, 16) + + 2 * PRIV_STACK_GUARD_SZ; + priv_stack_ptr = __alloc_percpu_gfp(priv_stack_alloc_size, 16, GFP_KERNEL); + if (!priv_stack_ptr) { + fp = org_fp; + goto out_priv_stack; + } + + priv_stack_init_guard(priv_stack_ptr, priv_stack_alloc_size); + fp->aux->priv_stack_ptr = priv_stack_ptr; + } + flen = fp->len; addrs = jit_data->addrs; if (addrs) { @@ -209,6 +264,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) cgctx.is_subprog = bpf_is_subprog(fp); cgctx.exception_boundary = fp->aux->exception_boundary; cgctx.exception_cb = fp->aux->exception_cb; + cgctx.priv_sp = priv_stack_ptr; /* Scouting faux-generate pass 0 */ if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) { @@ -306,6 +362,11 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) } bpf_prog_fill_jited_linfo(fp, addrs); out_addrs: + if (!image && priv_stack_ptr) { + fp->aux->priv_stack_ptr = NULL; + free_percpu(priv_stack_ptr); + } +out_priv_stack: kfree(addrs); kfree(jit_data); fp->aux->jit_data = NULL; @@ -419,6 +480,8 @@ void bpf_jit_free(struct bpf_prog *fp) if (fp->jited) { struct powerpc_jit_data *jit_data = fp->aux->jit_data; struct bpf_binary_header *hdr; + void __percpu *priv_stack_ptr; + int priv_stack_alloc_size; /* * If we fail the final pass of JIT (from jit_subprogs), @@ -432,6 +495,13 @@ void bpf_jit_free(struct bpf_prog *fp) } hdr = bpf_jit_binary_pack_hdr(fp); bpf_jit_binary_pack_free(hdr, NULL); + priv_stack_ptr = fp->aux->priv_stack_ptr; + if (priv_stack_ptr) { + priv_stack_alloc_size = round_up(fp->aux->stack_depth, 16) + + 2 * PRIV_STACK_GUARD_SZ; + priv_stack_check_guard(priv_stack_ptr, priv_stack_alloc_size, fp); + free_percpu(priv_stack_ptr); + } WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(fp)); } @@ -453,6 +523,11 @@ bool bpf_jit_supports_kfunc_call(void) return true; } +bool bpf_jit_supports_private_stack(void) +{ + return IS_ENABLED(CONFIG_PPC64); +} + bool bpf_jit_supports_arena(void) { return IS_ENABLED(CONFIG_PPC64); diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 640b84409687..d026cff30d1d 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -183,6 +183,22 @@ void bpf_jit_realloc_regs(struct codegen_context *ctx) { } +static void emit_fp_priv_stack(u32 *image, struct codegen_context *ctx) +{ + /* Load percpu data offset */ + EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), _R13, + offsetof(struct paca_struct, data_offset))); + PPC_LI64(bpf_to_ppc(BPF_REG_FP), (__force long)ctx->priv_sp); + /* + * Load base percpu pointer of private stack allocation. + * Runtime per-cpu address = (base + data_offset) + (guard + stack_size) + */ + EMIT(PPC_RAW_ADD(bpf_to_ppc(BPF_REG_FP), + bpf_to_ppc(TMP_REG_1), bpf_to_ppc(BPF_REG_FP))); + EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), bpf_to_ppc(BPF_REG_FP), + PRIV_STACK_GUARD_SZ + round_up(ctx->stack_size, 16))); +} + /* * For exception boundary & exception_cb progs: * return increased size to accommodate additional NVRs. @@ -251,7 +267,7 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) } EMIT(PPC_RAW_STDU(_R1, _R1, - -(bpf_jit_stack_size(ctx) + ctx->stack_size))); + -(bpf_jit_stack_size(ctx) + (ctx->priv_sp ? 0 : ctx->stack_size)))); } /* @@ -307,9 +323,16 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) * Exception_cb not restricted from using stack area or arena. * Setup frame pointer to point to the bpf stack area */ - if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP))) - EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1, - STACK_FRAME_MIN_SIZE + ctx->stack_size)); + if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP))) { + if (ctx->priv_sp) { + /* Set up fp in private stack */ + emit_fp_priv_stack(image, ctx); + } else { + /* Setup frame pointer to point to the bpf stack area */ + EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1, + STACK_FRAME_MIN_SIZE + ctx->stack_size)); + } + } if (ctx->arena_vm_start) PPC_LI64(bpf_to_ppc(ARENA_VM_START), ctx->arena_vm_start); @@ -339,7 +362,8 @@ static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx /* Tear down our stack frame */ if (bpf_has_stack_frame(ctx)) { - EMIT(PPC_RAW_ADDI(_R1, _R1, bpf_jit_stack_size(ctx) + ctx->stack_size)); + EMIT(PPC_RAW_ADDI(_R1, _R1, + bpf_jit_stack_size(ctx) + (ctx->priv_sp ? 0 : ctx->stack_size))); if (ctx->seen & SEEN_FUNC || ctx->exception_cb) { EMIT(PPC_RAW_LD(_R0, _R1, PPC_LR_STKOFF)); -- 2.52.0