From: Pawan Gupta Date: Tue, 30 Jun 2026 05:38:23 +0000 (-0700) Subject: bpf: Restrict JIT predictor flush to cBPF X-Git-Tag: v7.2-rc2~20^2~3 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0bb99f2cfaae6822d734d69722de30af823efdf3;p=thirdparty%2Fkernel%2Flinux.git bpf: Restrict JIT predictor flush to cBPF Currently predictor flush on memory reuse is done for all BPF JIT allocations, but only cBPF programs can be loaded by an unprivileged user. eBPF is privileged by default, and flushing predictors for all CPUs on every eBPF reuse penalizes the common case for no security benefit. eBPF allocations can be frequent on busy systems, only flush predictors for cBPF programs. Trampoline and dispatcher allocations also skip the flush as they are eBPF-only. Signed-off-by: Pawan Gupta Acked-by: Daniel Borkmann Signed-off-by: Daniel Borkmann --- diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index f6bcc0e1a950d..b0075ece4a6e7 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -2177,7 +2177,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr image_size = extable_offset + extable_size; ro_header = bpf_jit_binary_pack_alloc(image_size, &ro_image_ptr, sizeof(u64), &header, &image_ptr, - jit_fill_hole); + jit_fill_hole, was_classic); if (!ro_header) goto out_off; @@ -2870,7 +2870,7 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags, void *arch_alloc_bpf_trampoline(unsigned int size) { - return bpf_prog_pack_alloc(size, jit_fill_hole); + return bpf_prog_pack_alloc(size, jit_fill_hole, false); } void arch_free_bpf_trampoline(void *image, unsigned int size) diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c index 058ffbbaad856..3f3f0335d63c8 100644 --- a/arch/loongarch/net/bpf_jit.c +++ b/arch/loongarch/net/bpf_jit.c @@ -1762,7 +1762,7 @@ static int invoke_bpf(struct jit_ctx *ctx, struct bpf_tramp_nodes *tn, void *arch_alloc_bpf_trampoline(unsigned int size) { - return bpf_prog_pack_alloc(size, jit_fill_hole); + return bpf_prog_pack_alloc(size, jit_fill_hole, false); } void arch_free_bpf_trampoline(void *image, unsigned int size) @@ -2228,7 +2228,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr image_size = prog_size + extable_size; /* Now we know the size of the structure to make */ ro_header = bpf_jit_binary_pack_alloc(image_size, &ro_image_ptr, sizeof(u32), - &header, &image_ptr, jit_fill_hole); + &header, &image_ptr, jit_fill_hole, + bpf_prog_was_classic(prog)); if (!ro_header) goto out_offset; diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index d4a17e18c9fba..7b07b43575f11 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -295,7 +295,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr alloclen = proglen + FUNCTION_DESCR_SIZE + fixup_len + extable_len; fhdr = bpf_jit_binary_pack_alloc(alloclen, &fimage, 4, &hdr, &image, - bpf_jit_fill_ill_insns); + bpf_jit_fill_ill_insns, bpf_prog_was_classic(fp)); if (!fhdr) goto out_err; @@ -588,7 +588,7 @@ bool bpf_jit_inlines_helper_call(s32 imm) void *arch_alloc_bpf_trampoline(unsigned int size) { - return bpf_prog_pack_alloc(size, bpf_jit_fill_ill_insns); + return bpf_prog_pack_alloc(size, bpf_jit_fill_ill_insns, false); } void arch_free_bpf_trampoline(void *image, unsigned int size) diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c index c03c1de16b79a..f9d5347ba966b 100644 --- a/arch/riscv/net/bpf_jit_comp64.c +++ b/arch/riscv/net/bpf_jit_comp64.c @@ -1321,7 +1321,7 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags, void *arch_alloc_bpf_trampoline(unsigned int size) { - return bpf_prog_pack_alloc(size, bpf_fill_ill_insns); + return bpf_prog_pack_alloc(size, bpf_fill_ill_insns, false); } void arch_free_bpf_trampoline(void *image, unsigned int size) diff --git a/arch/riscv/net/bpf_jit_core.c b/arch/riscv/net/bpf_jit_core.c index 4365d07aaf547..ce3bd3762e08c 100644 --- a/arch/riscv/net/bpf_jit_core.c +++ b/arch/riscv/net/bpf_jit_core.c @@ -109,7 +109,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr bpf_jit_binary_pack_alloc(prog_size + extable_size, &jit_data->ro_image, sizeof(u32), &jit_data->header, &jit_data->image, - bpf_fill_ill_insns); + bpf_fill_ill_insns, + bpf_prog_was_classic(prog)); if (!jit_data->ro_header) goto out_offset; diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 054e043ffcd22..de7515ea1beae 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -3653,7 +3653,7 @@ cleanup: void *arch_alloc_bpf_trampoline(unsigned int size) { - return bpf_prog_pack_alloc(size, jit_fill_hole); + return bpf_prog_pack_alloc(size, jit_fill_hole, false); } void arch_free_bpf_trampoline(void *image, unsigned int size) @@ -3965,7 +3965,8 @@ out_image: /* allocate module memory for x86 insns and extable */ header = bpf_jit_binary_pack_alloc(roundup(proglen, align) + extable_size, &image, align, &rw_header, &rw_image, - jit_fill_hole); + jit_fill_hole, + bpf_prog_was_classic(prog)); if (!header) goto out_addrs; prog->aux->extable = (void *) image + roundup(proglen, align); diff --git a/include/linux/filter.h b/include/linux/filter.h index f68694f94ee78..14acb2455746f 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -1338,7 +1338,7 @@ void bpf_jit_free(struct bpf_prog *fp); struct bpf_binary_header * bpf_jit_binary_pack_hdr(const struct bpf_prog *fp); -void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns); +void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns, bool was_classic); void bpf_prog_pack_free(void *ptr, u32 size); static inline bool bpf_prog_kallsyms_verify_off(const struct bpf_prog *fp) @@ -1352,7 +1352,8 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **ro_image, unsigned int alignment, struct bpf_binary_header **rw_hdr, u8 **rw_image, - bpf_jit_fill_hole_t bpf_fill_ill_insns); + bpf_jit_fill_hole_t bpf_fill_ill_insns, + bool was_classic); int bpf_jit_binary_pack_finalize(struct bpf_binary_header *ro_header, struct bpf_binary_header *rw_header); void bpf_jit_binary_pack_free(struct bpf_binary_header *ro_header, diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 7f0a17f128d4e..1614ccc3f1111 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -942,7 +942,7 @@ out: return NULL; } -void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns) +void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns, bool was_classic) { unsigned int nbits = BPF_PROG_SIZE_TO_NBITS(size); struct bpf_prog_pack *pack; @@ -957,7 +957,7 @@ void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns) * safe because cBPF programs (the unprivileged attack surface) * are bounded well below a pack size. */ - if (static_branch_unlikely(&bpf_pred_flush_enabled)) + if (was_classic && static_branch_unlikely(&bpf_pred_flush_enabled)) pr_warn_once("BPF: Predictors not flushed for allocations greater than BPF_PROG_PACK_SIZE\n"); size = round_up(size, PAGE_SIZE); ptr = bpf_jit_alloc_exec(size); @@ -989,7 +989,9 @@ void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns) pos = 0; found_free_area: - static_call_cond(bpf_arch_pred_flush)(); + /* Flush only for cBPF as it may contain a crafted gadget */ + if (static_branch_unlikely(&bpf_pred_flush_enabled) && was_classic) + static_call_cond(bpf_arch_pred_flush)(); bitmap_set(pack->bitmap, pos, nbits); ptr = (void *)(pack->ptr) + (pos << BPF_PROG_CHUNK_SHIFT); @@ -1149,7 +1151,8 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **image_ptr, unsigned int alignment, struct bpf_binary_header **rw_header, u8 **rw_image, - bpf_jit_fill_hole_t bpf_fill_ill_insns) + bpf_jit_fill_hole_t bpf_fill_ill_insns, + bool was_classic) { struct bpf_binary_header *ro_header; u32 size, hole, start; @@ -1162,7 +1165,7 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **image_ptr, if (bpf_jit_charge_modmem(size)) return NULL; - ro_header = bpf_prog_pack_alloc(size, bpf_fill_ill_insns); + ro_header = bpf_prog_pack_alloc(size, bpf_fill_ill_insns, was_classic); if (!ro_header) { bpf_jit_uncharge_modmem(size); return NULL; diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c index b77db7413f8c7..ea2d60dc1feeb 100644 --- a/kernel/bpf/dispatcher.c +++ b/kernel/bpf/dispatcher.c @@ -145,7 +145,7 @@ void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from, mutex_lock(&d->mutex); if (!d->image) { - d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero); + d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero, false); if (!d->image) goto out; d->rw_image = bpf_jit_alloc_exec(PAGE_SIZE);