netdev - [PATCH bpf] bpf: fix default unprivileged allocation limit

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Message-Id: <20181206092732.4206-1-sandipan@linux.ibm.com>
Date:   Thu,  6 Dec 2018 14:57:32 +0530
From:   Sandipan Das <sandipan@...ux.ibm.com>
To:     daniel@...earbox.net, ast@...nel.org
Cc:     netdev@...r.kernel.org, linuxppc-dev@...abs.org,
        mpe@...erman.id.au, naveen.n.rao@...ux.ibm.com
Subject: [PATCH bpf] bpf: fix default unprivileged allocation limit

When using a large page size, the default value of the bpf_jit_limit
knob becomes invalid and users are not able to run unprivileged bpf
programs.

The bpf_jit_limit knob is represented internally as a 32-bit signed
integer because of which the default value, i.e. PAGE_SIZE * 40000,
overflows in case of an architecture like powerpc64 which uses 64K
as the default page size (i.e. CONFIG_PPC_64K_PAGES is set).

So, instead of depending on the page size, use a constant value.

Fixes: ede95a63b5e8 ("bpf: add bpf_jit_limit knob to restrict unpriv allocations")
Signed-off-by: Sandipan Das <sandipan@...ux.ibm.com>
---
 kernel/bpf/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index b1a3545d0ec8..a81d097a17fb 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -365,7 +365,7 @@ void bpf_prog_kallsyms_del_all(struct bpf_prog *fp)
 }

 #ifdef CONFIG_BPF_JIT
-# define BPF_JIT_LIMIT_DEFAULT	(PAGE_SIZE * 40000)
+# define BPF_JIT_LIMIT_DEFAULT	(4096 * 40000)

 /* All BPF JIT sysctl knobs here. */
 int bpf_jit_enable   __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_ALWAYS_ON);
-- 
2.19.2