linux-kernel - [PATCH v2 1/2] bpf: add __weak hook for allocating executable memory

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Date:   Wed, 21 Nov 2018 14:17:32 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Jessica Yu <jeyu@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH v2 1/2] bpf: add __weak hook for allocating executable memory

By default, BPF uses module_alloc() to allocate executable memory,
but this is not necessary on all arches and potentially undesirable
on some of them.

So break out the module_alloc() and module_memfree() calls into __weak
functions to allow them to be overridden in arch code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 kernel/bpf/core.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 1a796e0799ec..f28d8a5eb6b8 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -609,6 +609,16 @@ static void bpf_jit_uncharge_modmem(u32 pages)
 	atomic_long_sub(pages, &bpf_jit_current);
 }
 
+void *__weak bpf_jit_alloc_exec(unsigned long size)
+{
+	return module_alloc(size);
+}
+
+void __weak bpf_jit_free_exec(const void *addr)
+{
+	return module_memfree(size);
+}
+
 struct bpf_binary_header *
 bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
 		     unsigned int alignment,
@@ -626,7 +636,7 @@ bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
 
 	if (bpf_jit_charge_modmem(pages))
 		return NULL;
-	hdr = module_alloc(size);
+	hdr = bpf_jit_alloc_exec(size);
 	if (!hdr) {
 		bpf_jit_uncharge_modmem(pages);
 		return NULL;
@@ -650,7 +660,7 @@ void bpf_jit_binary_free(struct bpf_binary_header *hdr)
 {
 	u32 pages = hdr->pages;
 
-	module_memfree(hdr);
+	bpf_jit_free_exec(hdr);
 	bpf_jit_uncharge_modmem(pages);
 }
 
-- 
2.17.1