On Wed, Sep 01, 2021 at 01:31:18PM +0200, Greg KH wrote:
> On Wed, Sep 01, 2021 at 01:30:37PM +0200, Greg KH wrote:
> > On Mon, Aug 30, 2021 at 03:32:08PM -0300, Thadeu Lima de Souza Cascardo wrote:
> > > From: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > >
> > > Partially undo old commit 144cd91c4c2b ("bpf: move tmp variable into ax
> > > register in interpreter"). The reason we need this here is because ax
> > > register will be used for holding temporary state for div/mod instruction
> > > which otherwise interpreter would corrupt. This will cause a small +8 byte
> > > stack increase for interpreter, but with the gain that we can use it from
> > > verifier rewrites as scratch register.
> > >
> > > Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > > Reviewed-by: John Fastabend <john.fastabend@xxxxxxxxx>
> > > [cascardo: This partial revert is needed in order to support using AX for
> > > the following two commits, as there is no JMP32 on 4.19.y]
> > > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
> > > ---
> > > kernel/bpf/core.c | 32 +++++++++++++++-----------------
> > > 1 file changed, 15 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > > index e7211b0fa27c..30d871be9974 100644
> > > --- a/kernel/bpf/core.c
> > > +++ b/kernel/bpf/core.c
> > > @@ -616,9 +616,6 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
> > > * below.
> > > *
> > > * Constant blinding is only used by JITs, not in the interpreter.
> > > - * The interpreter uses AX in some occasions as a local temporary
> > > - * register e.g. in DIV or MOD instructions.
> > > - *
> > > * In restricted circumstances, the verifier can also use the AX
> > > * register for rewrites as long as they do not interfere with
> > > * the above cases!
> > > @@ -951,6 +948,7 @@ static unsigned int ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn,
> > > u32 tail_call_cnt = 0;
> > > void *ptr;
> > > int off;
> > > + u64 tmp;
> > >
> > > #define CONT ({ insn++; goto select_insn; })
> > > #define CONT_JMP ({ insn++; goto select_insn; })
> > > @@ -1013,22 +1011,22 @@ static unsigned int ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn,
> > > ALU64_MOD_X:
> > > if (unlikely(SRC == 0))
> > > return 0;
> > > - div64_u64_rem(DST, SRC, &AX);
> > > - DST = AX;
> > > + div64_u64_rem(DST, SRC, &tmp);
> > > + DST = tmp;
> > > CONT;
> > > ALU_MOD_X:
> > > if (unlikely((u32)SRC == 0))
> > > return 0;
> > > - AX = (u32) DST;
> > > - DST = do_div(AX, (u32) SRC);
> > > + tmp = (u32) DST;
> > > + DST = do_div(tmp, (u32) SRC);
> > > CONT;
> > > ALU64_MOD_K:
> > > - div64_u64_rem(DST, IMM, &AX);
> > > - DST = AX;
> > > + div64_u64_rem(DST, IMM, &tmp);
> > > + DST = tmp;
> > > CONT;
> > > ALU_MOD_K:
> > > - AX = (u32) DST;
> > > - DST = do_div(AX, (u32) IMM);
> > > + tmp = (u32) DST;
> > > + DST = do_div(tmp, (u32) IMM);
> > > CONT;
> > > ALU64_DIV_X:
> > > if (unlikely(SRC == 0))
> > > @@ -1038,17 +1036,17 @@ static unsigned int ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn,
> > > ALU_DIV_X:
> > > if (unlikely((u32)SRC == 0))
> > > return 0;
> > > - AX = (u32) DST;
> > > - do_div(AX, (u32) SRC);
> > > - DST = (u32) AX;
> > > + tmp = (u32) DST;
> > > + do_div(tmp, (u32) SRC);
> > > + DST = (u32) tmp;
> > > CONT;
> > > ALU64_DIV_K:
> > > DST = div64_u64(DST, IMM);
> > > CONT;
> > > ALU_DIV_K:
> > > - AX = (u32) DST;
> > > - do_div(AX, (u32) IMM);
> > > - DST = (u32) AX;
> > > + tmp = (u32) DST;
> > > + do_div(tmp, (u32) IMM);
> > > + DST = (u32) tmp;
> > > CONT;
> > > ALU_END_TO_BE:
> > > switch (IMM) {
> > > --
> > > 2.30.2
> > >
> >
> > Oops, no, this patch causes build errors:
> >
> > kernel/bpf/core.c: In function ‘___bpf_prog_run’:
> > kernel/bpf/core.c:951:13: error: redeclaration of ‘tmp’ with no linkage
> > 951 | u64 tmp;
> > | ^~~
> > kernel/bpf/core.c:839:13: note: previous declaration of ‘tmp’ with type ‘u64’ {aka ‘long long unsigned int’}
> > 839 | u64 tmp;
> > | ^~~
> > make[2]: *** [scripts/Makefile.build:329: kernel/bpf/core.o] Error 1
> >
> >
> > Please fix up and resend the whole series, as I will go drop these 3
> > patches from the 4.14.y queue now.
>
> All _4_ patches I mean. now dropped...
Ah... it seems I only built it with CONFIG_BPF_JIT_ALWAYS_ON. I will build with
both that option on and off and check the results.
Thanks for catching this.
Cascardo.
