[PATCH v4 1/2] powerpc64/bpf: Implement JIT support for private stack
adubey at linux.ibm.com
adubey at linux.ibm.com
Thu Feb 26 14:13:23 AEDT 2026
From: Abhishek Dubey <adubey at linux.ibm.com>
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
v2->v3:
Fix ci-bot bug targeting clobbered NVRs on stack rollback
v3->v4:
Added new field to fix priv_stack allocation
[v3]: https://lore.kernel.org/bpf/20260226005440.9570-1-adubey@linux.ibm.com
[v2]: https://lore.kernel.org/bpf/20260225153950.15331-1-adubey@linux.ibm.com
[v1]: https://lore.kernel.org/bpf/20260216152234.36632-1-adubey@linux.ibm.com
Signed-off-by: Abhishek Dubey <adubey at linux.ibm.com>
---
arch/powerpc/net/bpf_jit.h | 6 ++
arch/powerpc/net/bpf_jit_comp.c | 97 +++++++++++++++++++++++++++++--
arch/powerpc/net/bpf_jit_comp64.c | 29 ++++++++-
3 files changed, 124 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 7354e1d72f79..a232f3fb73be 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -178,8 +178,14 @@ struct codegen_context {
bool is_subprog;
bool exception_boundary;
bool exception_cb;
+ void __percpu *priv_sp;
+ unsigned int priv_stack_size;
};
+/* 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..ad70c3e1294e 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -129,25 +129,60 @@ 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 %s\n",
+ bpf_jit_get_prog_name(fp));
+ break;
+ }
+ }
+}
+
struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
{
u32 proglen;
u32 alloclen;
u8 *image = NULL;
- u32 *code_base;
- u32 *addrs;
- struct powerpc_jit_data *jit_data;
+ u32 *code_base = NULL;
+ u32 *addrs = NULL;
+ struct powerpc_jit_data *jit_data = NULL;
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;
- struct bpf_prog *tmp_fp;
+ struct bpf_prog *tmp_fp = NULL;
bool bpf_blinded = false;
bool extra_pass = false;
u8 *fimage = NULL;
- u32 *fcode_base;
+ u32 *fcode_base = NULL;
u32 extable_len;
u32 fixup_len;
@@ -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 +264,19 @@ 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;
+ cgctx.priv_stack_size = 0;
+ if (priv_stack_ptr) {
+ /*
+ * priv_stack_size required for setting bpf FP inside
+ * percpu allocation.
+ * stack_size is marked 0 to prevent allocation on
+ * general stack and offset calculation don't go for
+ * a toss in bpf_jit_stack_offsetof() & bpf_jit_stack_local()
+ */
+ cgctx.priv_stack_size = cgctx.stack_size;
+ cgctx.stack_size = 0;
+ }
/* Scouting faux-generate pass 0 */
if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
@@ -306,6 +374,11 @@ 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 +492,8 @@ 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 +507,13 @@ 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 +535,11 @@ 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..4d997da242fe 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->priv_stack_size, 16)));
+}
+
/*
* For exception boundary & exception_cb progs:
* return increased size to accommodate additional NVRs.
@@ -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);
--
2.52.0
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