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UPSTREAM: bpf, x86, arm64: Enable jit by default when not built as always-on

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After Spectre 2 fix via 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON
config") most major distros use BPF_JIT_ALWAYS_ON configuration these days
which compiles out the BPF interpreter entirely and always enables the
JIT. Also given recent fix in e1608f3fa857 ("bpf: Avoid setting bpf insns
pages read-only when prog is jited"), we additionally avoid fragmenting
the direct map for the BPF insns pages sitting in the general data heap
since they are not used during execution. Latter is only needed when run
through the interpreter.

Since both x86 and arm64 JITs have seen a lot of exposure over the years,
are generally most up to date and maintained, there is more downside in
!BPF_JIT_ALWAYS_ON configurations to have the interpreter enabled by default
rather than the JIT. Add a ARCH_WANT_DEFAULT_BPF_JIT config which archs can
use to set the bpf_jit_{enable,kallsyms} to 1. Back in the days the
bpf_jit_kallsyms knob was set to 0 by default since major distros still
had /proc/kallsyms addresses exposed to unprivileged user space which is
not the case anymore. Hence both knobs are set via BPF_JIT_DEFAULT_ON which
is set to 'y' in case of BPF_JIT_ALWAYS_ON or ARCH_WANT_DEFAULT_BPF_JIT.

Change-Id: I45eebc988228a01ef3ff66018f167eb68aaa6bc1
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/f78ad24795c2966efcc2ee19025fa3459f622185.1575903816.git.daniel@iogearbox.net
Signed-off-by: Sorayukii <sorayukii69@gmail.com>
This commit is contained in:
Daniel Borkmann 2019-12-09 16:08:03 +01:00 • committed by Sorayukii
commit 181fe66dd5
4 changed files with 11 additions and 1 deletions
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1
arch/arm64/Kconfig
View file

@ -38,6 +38,7 @@ config ARM64
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_NUMA_BALANCING
select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
select ARCH_WANT_DEFAULT_BPF_JIT
select ARCH_WANT_FRAME_POINTERS
select ARCH_HAS_UBSAN_SANITIZE_ALL
select ARCH_HAS_SET_MEMORY

1
arch/x86/Kconfig
View file

@ -47,6 +47,7 @@ config X86
select ARCH_USE_QUEUED_RWLOCKS
select ARCH_USE_QUEUED_SPINLOCKS
select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
select ARCH_WANT_DEFAULT_BPF_JIT if X86_64
select ARCH_WANTS_DYNAMIC_TASK_STRUCT
select ARCH_WANT_FRAME_POINTERS
select ARCH_WANT_IPC_PARSE_VERSION if X86_32

7
init/Kconfig
View file

@ -1517,6 +1517,9 @@ config BPF_SYSCALL
Enable the bpf() system call that allows to manipulate eBPF
programs and maps via file descriptors.
config ARCH_WANT_DEFAULT_BPF_JIT
bool
config BPF_JIT_ALWAYS_ON
bool "Permanently enable BPF JIT and remove BPF interpreter"
depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
@ -1534,6 +1537,10 @@ config BPF_UNPRIV_DEFAULT_OFF
disable it by setting it to 1 (from which no other transition to
0 is possible anymore).
config BPF_JIT_DEFAULT_ON
def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON
depends on HAVE_EBPF_JIT && BPF_JIT
config USERFAULTFD
bool "Enable userfaultfd() system call"
depends on MMU

3
kernel/bpf/core.c
View file

@ -533,7 +533,8 @@ void bpf_prog_kallsyms_del_all(struct bpf_prog *fp)
#ifdef CONFIG_BPF_JIT
/* All BPF JIT sysctl knobs here. */
int bpf_jit_enable __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_ALWAYS_ON);
int bpf_jit_enable __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
int bpf_jit_kallsyms __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
int bpf_jit_harden __read_mostly;
long bpf_jit_limit __read_mostly;
long bpf_jit_limit_max __read_mostly;