linux-kernel - Re: [PATCH bpf-next 04/13] uprobes: Add arch_uprobe_verify

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Message-ID: <Z1w0z2KSgFGggAVD@krava>
Date: Fri, 13 Dec 2024 14:21:19 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Alan Maguire <alan.maguire@...cle.com>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 04/13] uprobes: Add arch_uprobe_verify_opcode
 function

On Thu, Dec 12, 2024 at 04:48:05PM -0800, Andrii Nakryiko wrote:
> On Wed, Dec 11, 2024 at 5:34 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Adding arch_uprobe_verify_opcode function, so we can overload
> > verification for each architecture in following changes.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  include/linux/uprobes.h |  5 +++++
> >  kernel/events/uprobes.c | 19 ++++++++++++++++---
> >  2 files changed, 21 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> > index cc723bc48c1d..8843b7f99ed0 100644
> > --- a/include/linux/uprobes.h
> > +++ b/include/linux/uprobes.h
> > @@ -215,6 +215,11 @@ extern void uprobe_handle_trampoline(struct pt_regs *regs);
> >  extern void *arch_uretprobe_trampoline(unsigned long *psize);
> >  extern unsigned long uprobe_get_trampoline_vaddr(void);
> >  extern void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len);
> > +extern int uprobe_verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode);
> > +extern int arch_uprobe_verify_opcode(struct arch_uprobe *auprobe, struct page *page,
> > +                                    unsigned long vaddr, uprobe_opcode_t *new_opcode,
> > +                                    int nbytes);
> > +extern bool arch_uprobe_is_register(uprobe_opcode_t *insn, int nbytes);
> >  #else /* !CONFIG_UPROBES */
> >  struct uprobes_state {
> >  };
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 7c2ecf11a573..8068f91de9e3 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -263,7 +263,13 @@ static void uprobe_copy_to_page(struct page *page, unsigned long vaddr, const vo
> >         kunmap_atomic(kaddr);
> >  }
> >
> > -static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
> > +__weak bool arch_uprobe_is_register(uprobe_opcode_t *insn, int nbytes)
> > +{
> > +       return is_swbp_insn(insn);
> 
> a bit weird that we ignore nbytes here... should we have nbytes ==
> UPROBE_SWBP_INSN_SIZE check somewhere here or inside is_swbp_insn()?

the original is_swbp_insn function does not need that and we need
nbytes in the overloaded arch_uprobe_is_register to distinguish
between 1 byte and 5 byte update..

jirka

> 
> > +}
> > +
> > +int uprobe_verify_opcode(struct page *page, unsigned long vaddr,
> > +                        uprobe_opcode_t *new_opcode)
> >  {
> >         uprobe_opcode_t old_opcode;
> >         bool is_swbp;
> > @@ -291,6 +297,13 @@ static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t
> >         return 1;
> >  }
> >
> > +__weak int arch_uprobe_verify_opcode(struct arch_uprobe *auprobe, struct page *page,
> > +                                    unsigned long vaddr, uprobe_opcode_t *new_opcode,
> > +                                    int nbytes)
> > +{
> > +       return uprobe_verify_opcode(page, vaddr, new_opcode);
> 
> again, dropping nbytes on the floor here
> 
> > +}
> > +
> >  static struct delayed_uprobe *
> >  delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
> >  {
> > @@ -479,7 +492,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >         bool orig_page_huge = false;
> >         unsigned int gup_flags = FOLL_FORCE;
> >
> > -       is_register = is_swbp_insn(insn);
> > +       is_register = arch_uprobe_is_register(insn, nbytes);
> >         uprobe = container_of(auprobe, struct uprobe, arch);
> >
> >  retry:
> > @@ -490,7 +503,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >         if (IS_ERR(old_page))
> >                 return PTR_ERR(old_page);
> >
> > -       ret = verify_opcode(old_page, vaddr, insn);
> > +       ret = arch_uprobe_verify_opcode(auprobe, old_page, vaddr, insn, nbytes);
> >         if (ret <= 0)
> >                 goto put_old;
> >
> > --
> > 2.47.0
> >