A program on a private stack keeps its BPF frames in a per-CPU area of its own rather than on the kernel stack of whichever context entered it. bpf_enable_priv_stack() grants that mode only once the JIT reports bpf_jit_supports_private_stack(), which riscv64 did not: programs there always ran on the kernel stack, and a struct_ops program that requires one was rejected with -EACCES. Allocate a per-CPU area of the verifier calculated depth plus a 16 byte guard region at each end, and point BPF_REG_FP (S5) at the top of it while leaving SP on the kernel stack. Every BPF stack access already goes through S5, and S5 is callee-saved with each subprog deriving its own, so nothing else in the JIT has to know about the private stack. The outgoing stack argument area stays in the kernel frame: callers write it relative to SP, callees relative to RV_REG_FP, which the prologue sets to the caller's SP. The per-CPU lookup is emitted after the tail call entry point: a program using a private stack can still be entered as a tail call target, and RV_TAILCALL_OFFSET is a constant added to the target's bpf_func, so what is in front of it must be the same size in every program. The base is materialized with absolute moves, as on arm64, x86-64 and powerpc64: the vmalloc'd per-CPU area is beyond an auipc pair from the JIT region, and riscv64 has no register holding the per-CPU offset, so the address of __per_cpu_offset is loaded too. emit_imm() is a choice there, not a requirement; emit_addr() as used by insn_is_mov_percpu_addr() would need an extra_pass argument and an error return in bpf_jit_build_prologue(), touching bpf_jit_comp32.c too. Both constants are fixed before the offset convergence loop, so the prologue length is stable across passes. The guard value follows arm64, x86-64 and powerpc64, and the 16 byte two-copy region at each end follows arm64 and powerpc64, since x86-64 uses an 8 byte guard with a single copy. A jited program has them checked when it is freed, reporting the first corrupted CPU only; failure paths release the area unchecked since the image never ran, which also clears priv_stack_ptr for the later bpf_jit_free(). RV32 does not declare support and keeps the existing kernel stack behaviour. Signed-off-by: Chen Pei --- arch/riscv/net/bpf_jit.h | 1 + arch/riscv/net/bpf_jit_comp64.c | 42 +++++++++++++++-- arch/riscv/net/bpf_jit_core.c | 84 +++++++++++++++++++++++++++++---- 3 files changed, 115 insertions(+), 12 deletions(-) diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h index 21a190a6a6d9..efab2b6803e4 100644 --- a/arch/riscv/net/bpf_jit.h +++ b/arch/riscv/net/bpf_jit.h @@ -14,6 +14,7 @@ #define RV_MAX_REG_ARGS 8 #define RV_EXTRA_STK_ARGS (RV_MAX_REG_ARGS - MAX_BPF_FUNC_REG_ARGS) +#define PRIV_STACK_GUARD_SZ 16 /* verify runtime detection extension status */ #define rv_ext_enabled(ext) \ diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c index 371405598faa..a7a7d2f9da85 100644 --- a/arch/riscv/net/bpf_jit_comp64.c +++ b/arch/riscv/net/bpf_jit_comp64.c @@ -2134,12 +2134,34 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx, return 0; } +static void emit_priv_stack_frame(struct rv_jit_context *ctx) +{ + u64 fp = (__force u64)ctx->prog->aux->priv_stack_ptr + PRIV_STACK_GUARD_SZ; + + fp += round_up(ctx->prog->aux->stack_depth, STACK_ALIGN); + emit_imm(RV_REG_S5, fp, ctx); +#ifdef CONFIG_SMP + emit_lw(RV_REG_T1, offsetof(struct thread_info, cpu), RV_REG_TP, ctx); + emit_imm(RV_REG_T2, (u64)__per_cpu_offset, ctx); + emit_sh3add(RV_REG_T1, RV_REG_T1, RV_REG_T2, ctx); + emit_ld(RV_REG_T1, 0, RV_REG_T1, ctx); + emit_add(RV_REG_S5, RV_REG_S5, RV_REG_T1, ctx); +#endif +} + void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog) { + bool priv_stack = ctx->prog->aux->priv_stack_ptr; int i, stack_adjust = 0, store_offset, bpf_stack_adjust = ctx->stack_arg_sz; - bpf_stack_adjust += round_up(ctx->prog->aux->stack_depth, STACK_ALIGN); - if (bpf_stack_adjust) + /* + * With a private stack only the outgoing stack argument area is left in + * this frame. It has to stay: the caller writes it relative to SP while + * the callee reads it relative to RV_REG_FP, the caller's SP set below. + */ + if (!priv_stack) + bpf_stack_adjust += round_up(ctx->prog->aux->stack_depth, STACK_ALIGN); + if (bpf_stack_adjust || priv_stack) mark_fp(ctx); if (seen_reg(RV_REG_RA, ctx)) @@ -2217,7 +2239,16 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog) emit_addi(RV_REG_FP, RV_REG_SP, stack_adjust, ctx); - if (bpf_stack_adjust) + /* + * Point BPF_REG_FP at the top of this CPU's private stack. A program + * with one can still be entered as a tail call target, at + * RV_TAILCALL_OFFSET, so this has to come after that entry point; the + * offset is a constant added to the target's bpf_func, so everything in + * front of it must also be the same size in every program. + */ + if (priv_stack) + emit_priv_stack_frame(ctx); + else if (bpf_stack_adjust) emit_addi(RV_REG_S5, RV_REG_SP, bpf_stack_adjust, ctx); ctx->stack_size = stack_adjust; @@ -2320,3 +2351,8 @@ bool bpf_jit_supports_hmul(void) { return true; } + +bool bpf_jit_supports_private_stack(void) +{ + return true; +} diff --git a/arch/riscv/net/bpf_jit_core.c b/arch/riscv/net/bpf_jit_core.c index f2497ec7d378..f2021088e447 100644 --- a/arch/riscv/net/bpf_jit_core.c +++ b/arch/riscv/net/bpf_jit_core.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include "bpf_jit.h" @@ -44,6 +45,62 @@ bool bpf_jit_needs_zext(void) return true; } +#define PRIV_STACK_GUARD_VAL 0xEB9F12345678eb9fULL + +static u32 priv_stack_size(struct bpf_prog *prog) +{ + return round_up(prog->aux->stack_depth, STACK_ALIGN) + + 2 * PRIV_STACK_GUARD_SZ; +} + +static int alloc_priv_stack(struct bpf_prog *prog) +{ + u32 size = priv_stack_size(prog); + u32 end = (size - PRIV_STACK_GUARD_SZ) / sizeof(u64); + void __percpu *ptr; + int cpu, i; + + ptr = __alloc_percpu_gfp(size, STACK_ALIGN, GFP_KERNEL); + if (!ptr) + return -ENOMEM; + + for_each_possible_cpu(cpu) { + u64 *stack = per_cpu_ptr(ptr, cpu); + + for (i = 0; i < PRIV_STACK_GUARD_SZ / sizeof(u64); i++) { + stack[i] = PRIV_STACK_GUARD_VAL; + stack[end + i] = PRIV_STACK_GUARD_VAL; + } + } + prog->aux->priv_stack_ptr = ptr; + return 0; +} + +static void priv_stack_check_guard(struct bpf_prog *prog) +{ + u32 end = (priv_stack_size(prog) - PRIV_STACK_GUARD_SZ) / sizeof(u64); + int cpu; + + for_each_possible_cpu(cpu) { + u64 *stack = per_cpu_ptr(prog->aux->priv_stack_ptr, cpu); + + if (stack[0] != PRIV_STACK_GUARD_VAL || + stack[1] != PRIV_STACK_GUARD_VAL || + stack[end] != PRIV_STACK_GUARD_VAL || + stack[end + 1] != PRIV_STACK_GUARD_VAL) { + pr_err("bpf-jit: private stack overflow/underflow guard of prog %s corrupted on CPU %d\n", + bpf_jit_get_prog_name(prog), cpu); + return; + } + } +} + +static void free_priv_stack(struct bpf_prog *prog) +{ + free_percpu(prog->aux->priv_stack_ptr); + prog->aux->priv_stack_ptr = NULL; +} + struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_prog *prog) { unsigned int prog_size = 0, extable_size = 0; @@ -84,12 +141,15 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr round_up((stack_arg_cnt - RV_EXTRA_STK_ARGS) * 8, STACK_ALIGN) : 0; ctx->prog = prog; + if (prog->aux->jits_use_priv_stack && alloc_priv_stack(prog)) + goto out_free_hdr; + ctx->offset = kvzalloc_objs(int, prog->len); if (!ctx->offset) - goto out_offset; + goto out_free_hdr; if (build_body(ctx, extra_pass, NULL)) - goto out_offset; + goto out_free_hdr; for (i = 0; i < prog->len; i++) { prev_ninsns += 32; @@ -104,7 +164,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr ctx->prologue_len = ctx->ninsns; if (build_body(ctx, extra_pass, ctx->offset)) - goto out_offset; + goto out_free_hdr; ctx->epilogue_offset = ctx->ninsns; bpf_jit_build_epilogue(ctx); @@ -124,7 +184,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr bpf_fill_ill_insns, bpf_prog_was_classic(prog)); if (!jit_data->ro_header) - goto out_offset; + goto out_free_hdr; /* * Use the image(RW) for writing the JITed instructions. But also save @@ -190,10 +250,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr ctx->offset[i] = ctx->offset[i - 1]; ctx->offset[0] = ninsns_rvoff(ctx->prologue_len); bpf_prog_update_insn_ptrs(prog, ctx->offset, jit_data->ro_image); -out_offset: - kvfree(ctx->offset); - kfree(jit_data); - prog->aux->jit_data = NULL; + goto out_free_ctx; } return prog; @@ -209,7 +266,12 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr sizeof(jit_data->header->size)); bpf_jit_binary_pack_free(jit_data->ro_header, jit_data->header); } - goto out_offset; + free_priv_stack(prog); +out_free_ctx: + kvfree(ctx->offset); + kfree(jit_data); + prog->aux->jit_data = NULL; + return prog; } u64 bpf_jit_alloc_exec_limit(void) @@ -261,6 +323,10 @@ void bpf_jit_free(struct bpf_prog *prog) prog->bpf_func = (void *)prog->bpf_func - cfi_get_offset(); hdr = bpf_jit_binary_pack_hdr(prog); bpf_jit_binary_pack_free(hdr, NULL); + if (prog->aux->priv_stack_ptr) { + priv_stack_check_guard(prog); + free_priv_stack(prog); + } WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(prog)); } -- 2.50.1