bpf: fix default unprivileged allocation limit
Subsystems (4)
PATCH 1/1 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.
--- kernel/bpf/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/bpf/core.c +1 -1
@@ -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 );
Signature · 1 line
2.19.2
Quoting Sandipan Das (2018-12-06 03:27:32)
Quoted 4 lines
When using a large page size, the default value of the
bpf_jit_limitknob becomes invalid and users are not able to run unprivileged bpf programs.
Quoted 8 lines
The
bpf_jit_limitknob 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_PAGESis 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 10 lines
Signed-off-by Sandipan Das <[email protected]>--- kernel/bpf/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)kernel/bpf/core.c +0
-0
kernel/bpf/core.c void bpf_prog_kallsyms_del_all(struct bpf_prog *fp) · line 368
Quoted 5 lines
kernel/bpf/core.c +1
-1@@ -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.
Quoted 6 lines
kernel/bpf/core.c +0
-0/* All BPF JIT sysctl knobs here. */ int bpf_jit_enable__read_mostly =IS_BUILTIN (CONFIG_BPF_JIT_ALWAYS_ON );Signature · 1 line
2.19.2