linux-kernel - [PATCH bpf-next 3/5] bpf: introduce bpf_arch_text_invalidate for bpf_prog

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Date:   Sun, 15 May 2022 22:40:49 -0700
From:   Song Liu <song@...nel.org>
To:     <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <peterz@...radead.org>,
        <mcgrof@...nel.org>, <torvalds@...ux-foundation.org>,
        <rick.p.edgecombe@...el.com>, <kernel-team@...com>,
        Song Liu <song@...nel.org>
Subject: [PATCH bpf-next 3/5] bpf: introduce bpf_arch_text_invalidate for bpf_prog_pack

Introduce bpf_arch_text_invalidate and use it to fill unused part of the
bpf_prog_pack with illegal instructions when a BPF program is freed.

Signed-off-by: Song Liu <song@...nel.org>
---
 arch/x86/net/bpf_jit_comp.c | 5 +++++
 include/linux/bpf.h         | 1 +
 kernel/bpf/core.c           | 8 ++++++++
 3 files changed, 14 insertions(+)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index a2b6d197c226..f298b18a9a3d 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -228,6 +228,11 @@ static void jit_fill_hole(void *area, unsigned int size)
 	memset(area, 0xcc, size);
 }
 
+int bpf_arch_text_invalidate(void *dst, size_t len)
+{
+	return IS_ERR_OR_NULL(text_poke_set(dst, 0xcc, len));
+}
+
 struct jit_context {
 	int cleanup_addr; /* Epilogue code offset */
 
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5061ccd8b2dc..0288a6464236 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2362,6 +2362,7 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
 		       void *addr1, void *addr2);
 
 void *bpf_arch_text_copy(void *dst, void *src, size_t len);
+int bpf_arch_text_invalidate(void *dst, size_t len);
 
 struct btf_id_set;
 bool btf_id_set_contains(const struct btf_id_set *set, u32 id);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 2d0c9d4696ad..cacd8684c3c4 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -968,6 +968,9 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
 	nbits = BPF_PROG_SIZE_TO_NBITS(hdr->size);
 	pos = ((unsigned long)hdr - (unsigned long)pack_ptr) >> BPF_PROG_CHUNK_SHIFT;
 
+	WARN_ONCE(bpf_arch_text_invalidate(hdr, hdr->size),
+		  "bpf_prog_pack bug: missing bpf_arch_text_invalidate?\n");
+
 	bitmap_clear(pack->bitmap, pos, nbits);
 	if (bitmap_find_next_zero_area(pack->bitmap, bpf_prog_chunk_count(), 0,
 				       bpf_prog_chunk_count(), 0) == 0) {
@@ -2740,6 +2743,11 @@ void * __weak bpf_arch_text_copy(void *dst, void *src, size_t len)
 	return ERR_PTR(-ENOTSUPP);
 }
 
+int __weak bpf_arch_text_invalidate(void *dst, size_t len)
+{
+	return -ENOTSUPP;
+}
+
 DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 EXPORT_SYMBOL(bpf_stats_enabled_key);
 
-- 
2.30.2