arm64/bpf: Remove 128MB limit for BPF JIT programs

commit b89ddf4cca43f1269093942cf5c4e457fd45c335 upstream.

Commit 91fc957c9b1d ("arm64/bpf: don't allocate BPF JIT programs in module
memory") restricts BPF JIT program allocation to a 128MB region to ensure
BPF programs are still in branching range of each other. However this
restriction should not apply to the aarch64 JIT, since BPF_JMP | BPF_CALL
are implemented as a 64-bit move into a register and then a BLR instruction -
which has the effect of being able to call anything without proximity
limitation.

The practical reason to relax this restriction on JIT memory is that 128MB of
JIT memory can be quickly exhausted, especially where PAGE_SIZE is 64KB - one
page is needed per program. In cases where seccomp filters are applied to
multiple VMs on VM launch - such filters are classic BPF but converted to
BPF - this can severely limit the number of VMs that can be launched. In a
world where we support BPF JIT always on, turning off the JIT isn't always an
option either.

Fixes: 91fc957c9b1d ("arm64/bpf: don't allocate BPF JIT programs in module memory")
Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <russell.king@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/1636131046-5982-2-git-send-email-alan.maguire@oracle.com
Reviewed-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 0 insertions, 9 deletions

diff --git a/arch/arm64/include/asm/extable.h b/arch/arm64/include/asm/extable.h
index b15eb4a3e6b2..840a35ed92ec 100644
--- a/arch/arm64/include/asm/extable.h
+++ b/arch/arm64/include/asm/extable.h
@@ -22,15 +22,6 @@ struct exception_table_entry
 
 #define ARCH_HAS_RELATIVE_EXTABLE
 
-static inline bool in_bpf_jit(struct pt_regs *regs)
-{
-	if (!IS_ENABLED(CONFIG_BPF_JIT))
-		return false;
-
-	return regs->pc >= BPF_JIT_REGION_START &&
-	       regs->pc < BPF_JIT_REGION_END;
-}
-
 #ifdef CONFIG_BPF_JIT
 int arm64_bpf_fixup_exception(const struct exception_table_entry *ex,
 			      struct pt_regs *regs);