linux-kernel - [PATCH 3/4] bpf: add __weak hook for allocating executable memory

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Message-Id: <20181117185715.25198-4-ard.biesheuvel@linaro.org>
Date:   Sat, 17 Nov 2018 10:57:14 -0800
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-kernel@...r.kernel.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>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "David S. Miller" <davem@...emloft.net>,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
        netdev@...r.kernel.org
Subject: [PATCH 3/4] 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() call into a __weak function to allow
it to be overridden in arch code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 kernel/bpf/core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 29f766dac203..156d6b96ac6c 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -609,6 +609,11 @@ 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);
+}
+
 struct bpf_binary_header *
 bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
 		     unsigned int alignment,
@@ -626,7 +631,7 @@ 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;
-- 
2.17.1