Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Song Liu <song@kernel.org>
To:     <bpf@vger.kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
CC:     <andrii@kernel.org>, <ast@kernel.org>, <daniel@iogearbox.net>,
        <kernel-team@fb.com>, <hch@infradead.org>, <peterz@infradead.org>,
        <torvalds@linux-foundation.org>, Song Liu <song@kernel.org>
Subject: [PATCH v2 bpf 1/3] bpf: fill new bpf_prog_pack with illegal instructions
Date:   Mon, 25 Apr 2022 13:39:45 -0700
Message-ID: <20220425203947.3311308-2-song@kernel.org>
In-Reply-To: <20220425203947.3311308-1-song@kernel.org>
References: <20220425203947.3311308-1-song@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8BIT
Content-Type: text/plain
Precedence: bulk

bpf_prog_pack enables sharing huge pages among multiple BPF programs.
These pages are marked as executable before the JIT engine fill it with
BPF programs. To make these pages safe, fill the hole bpf_prog_pack with
illegal instructions before making it executable.

Fixes: 57631054fae6 ("bpf: Introduce bpf_prog_pack allocator")
Fixes: 33c9805860e5 ("bpf: Introduce bpf_jit_binary_pack_[alloc|finalize|free]")
Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/bpf/core.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 13e9dbeeedf3..132dfba389be 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -873,7 +873,7 @@ static size_t select_bpf_prog_pack_size(void)
 	return size;
 }
 
-static struct bpf_prog_pack *alloc_new_pack(void)
+static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_insns)
 {
 	struct bpf_prog_pack *pack;
 
@@ -886,6 +886,7 @@ static struct bpf_prog_pack *alloc_new_pack(void)
 		kfree(pack);
 		return NULL;
 	}
+	bpf_fill_ill_insns(pack->ptr, bpf_prog_pack_size);
 	bitmap_zero(pack->bitmap, bpf_prog_pack_size / BPF_PROG_CHUNK_SIZE);
 	list_add_tail(&pack->list, &pack_list);
 
@@ -895,7 +896,7 @@ static struct bpf_prog_pack *alloc_new_pack(void)
 	return pack;
 }
 
-static void *bpf_prog_pack_alloc(u32 size)
+static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
 {
 	unsigned int nbits = BPF_PROG_SIZE_TO_NBITS(size);
 	struct bpf_prog_pack *pack;
@@ -910,6 +911,7 @@ static void *bpf_prog_pack_alloc(u32 size)
 		size = round_up(size, PAGE_SIZE);
 		ptr = module_alloc(size);
 		if (ptr) {
+			bpf_fill_ill_insns(ptr, size);
 			set_vm_flush_reset_perms(ptr);
 			set_memory_ro((unsigned long)ptr, size / PAGE_SIZE);
 			set_memory_x((unsigned long)ptr, size / PAGE_SIZE);
@@ -923,7 +925,7 @@ static void *bpf_prog_pack_alloc(u32 size)
 			goto found_free_area;
 	}
 
-	pack = alloc_new_pack();
+	pack = alloc_new_pack(bpf_fill_ill_insns);
 	if (!pack)
 		goto out;
 
@@ -1102,7 +1104,7 @@ 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);
+	ro_header = bpf_prog_pack_alloc(size, bpf_fill_ill_insns);
 	if (!ro_header) {
 		bpf_jit_uncharge_modmem(size);
 		return NULL;
-- 
2.30.2