On Thu, Nov 07, 2019 at 10:37:19PM +0000, Song Liu wrote:
>
>
> > On Nov 6, 2019, at 9:46 PM, Alexei Starovoitov <ast@xxxxxxxxxx> wrote:
> >
>
> [...]
>
> >
> > Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> > ---
> > arch/x86/net/bpf_jit_comp.c | 227 ++++++++++++++++++++++++++++++--
> > include/linux/bpf.h | 98 ++++++++++++++
> > include/uapi/linux/bpf.h | 2 +
> > kernel/bpf/Makefile | 1 +
> > kernel/bpf/btf.c | 77 ++++++++++-
> > kernel/bpf/core.c | 1 +
> > kernel/bpf/syscall.c | 53 +++++++-
> > kernel/bpf/trampoline.c | 252 ++++++++++++++++++++++++++++++++++++
> > kernel/bpf/verifier.c | 39 ++++++
> > 9 files changed, 732 insertions(+), 18 deletions(-)
> > create mode 100644 kernel/bpf/trampoline.c
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 8631d3bd637f..44169e8bffc0 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -98,6 +98,7 @@ static int bpf_size_to_x86_bytes(int bpf_size)
> >
> > /* Pick a register outside of BPF range for JIT internal work */
> > #define AUX_REG (MAX_BPF_JIT_REG + 1)
> > +#define X86_REG_R9 (MAX_BPF_JIT_REG + 2)
> >
> > /*
> > * The following table maps BPF registers to x86-64 registers.
> > @@ -123,6 +124,7 @@ static const int reg2hex[] = {
> > [BPF_REG_FP] = 5, /* RBP readonly */
> > [BPF_REG_AX] = 2, /* R10 temp register */
> > [AUX_REG] = 3, /* R11 temp register */
> > + [X86_REG_R9] = 1, /* R9 register, 6th function argument */
>
> We should update the comment above this:
>
> * Also x86-64 register R9 is unused. ...
good point. fixed.
> > + /* One half of the page has active running trampoline.
> > + * Another half is an area for next trampoline.
> > + * Make sure the trampoline generation logic doesn't overflow.
> > + */
> > + if (WARN_ON_ONCE(prog - (u8 *)image > PAGE_SIZE / 2 - BPF_INSN_SAFETY))
> > + return -EFAULT;
>
> Given max number of args, can we catch this error at compile time?
I don't see how to do that. I was thinking about having fake __init function
that would call it with flags that can generate the longest trampoline, but
it's not fool proof either.
So I've added a test for it instead. See patch 10.
> > +
> > +static int bpf_trampoline_update(struct bpf_prog *prog)
>
> Seems argument "prog" is not used at all?
like one below ? ;)
> > +{
> > + struct bpf_trampoline *tr = prog->aux->trampoline;
> > + void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
> > + void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
> > + if (err)
> > + goto out;
> > + tr->selector++;
>
> Shall we do selector-- for unlink?
It's a bit flip. I think it would be more confusing with --
