On Thu, Jul 30, 2020 at 08:28:56AM -0400, Qian Cai wrote: > On Tue, Jul 28, 2020 at 05:21:26PM +0200, Jean-Philippe Brucker wrote: > > When a tracing BPF program attempts to read memory without using the > > bpf_probe_read() helper, the verifier marks the load instruction with > > the BPF_PROBE_MEM flag. Since the arm64 JIT does not currently recognize > > this flag it falls back to the interpreter. > > > > Add support for BPF_PROBE_MEM, by appending an exception table to the > > BPF program. If the load instruction causes a data abort, the fixup > > infrastructure finds the exception table and fixes up the fault, by > > clearing the destination register and jumping over the faulting > > instruction. > > > > To keep the compact exception table entry format, inspect the pc in > > fixup_exception(). A more generic solution would add a "handler" field > > to the table entry, like on x86 and s390. > > > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> > > This will fail to compile on arm64, > > https://gitlab.com/cailca/linux-mm/-/blob/master/arm64.config > > arch/arm64/mm/extable.o: In function `fixup_exception': > arch/arm64/mm/extable.c:19: undefined reference to `arm64_bpf_fixup_exception' Thanks for the report, I attached a fix. Daniel, can I squash it and resend as v2 or is it too late? I'd be more confident if my patches sat a little longer on the list so arm64 folks have a chance to review them. This isn't my first silly mistake... Thanks, Jean
>From 17d0f041b57903cb2657dde15559cd1923498337 Mon Sep 17 00:00:00 2001 From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> Date: Thu, 30 Jul 2020 14:45:44 +0200 Subject: [PATCH] arm64: bpf: Fix build for !CONFIG_BPF_JIT Add a stub for arm64_bpf_fixup_exception() when CONFIG_BPF_JIT isn't enabled, and avoid the fixup in this case. Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> --- arch/arm64/include/asm/extable.h | 9 +++++++++ arch/arm64/mm/extable.c | 3 ++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/extable.h b/arch/arm64/include/asm/extable.h index bcee40df1586..840a35ed92ec 100644 --- a/arch/arm64/include/asm/extable.h +++ b/arch/arm64/include/asm/extable.h @@ -22,8 +22,17 @@ struct exception_table_entry #define ARCH_HAS_RELATIVE_EXTABLE +#ifdef CONFIG_BPF_JIT int arm64_bpf_fixup_exception(const struct exception_table_entry *ex, struct pt_regs *regs); +#else /* !CONFIG_BPF_JIT */ +static inline +int arm64_bpf_fixup_exception(const struct exception_table_entry *ex, + struct pt_regs *regs) +{ + return 0; +} +#endif /* !CONFIG_BPF_JIT */ extern int fixup_exception(struct pt_regs *regs); #endif diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c index 1f42991cacdd..eee1732ab6cd 100644 --- a/arch/arm64/mm/extable.c +++ b/arch/arm64/mm/extable.c @@ -14,7 +14,8 @@ int fixup_exception(struct pt_regs *regs) if (!fixup) return 0; - if (regs->pc >= BPF_JIT_REGION_START && + if (IS_ENABLED(CONFIG_BPF_JIT) && + regs->pc >= BPF_JIT_REGION_START && regs->pc < BPF_JIT_REGION_END) return arm64_bpf_fixup_exception(fixup, regs); -- 2.27.0