Re: [PATCH bpf] bpf: fix default unprivileged allocation limit
From: Michael Roth <hidden>
Date: 2018-12-06 17:25:25
Also in:
linuxppc-dev
Quoting Sandipan Das (2018-12-06 03:27:32)
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")This also consistently caused a virtio-net KVM Ubuntu 18.04 guest to time out on configuring networking during boot via systemd/netplan. A bisect pointed to the same commit this patch addresses.
quoted hunk ↗ jump to hunk
Signed-off-by: Sandipan Das <redacted> --- 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)
This isn't quite right as we still use (bpf_jit_limit >> PAGE_SHIFT) to check allocations in bpf_jit_charge_modmem(), so that should be fixed up as well. Another alternative which is to clamp BPF_JIT_LIMIT_DEFAULT to INT_MAX, which fixes the issue for me and is similar to what bpf_jit_charge_init() does for kernels where MODULES_VADDR is defined. I'll go ahead and send the patch in case that seems preferable.
/* All BPF JIT sysctl knobs here. */ int bpf_jit_enable __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_ALWAYS_ON); -- 2.19.2