Messages in this thread | | | Date | Tue, 1 Mar 2022 11:49:05 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions |
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On Tue, 1 Mar 2022 00:25:13 +0100 Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Feb 28, 2022 at 03:07:05PM +0900, Masami Hiramatsu wrote: > > Hi Peter, > > > > So, instead of this change, can you try below? > > This introduce the arch_adjust_kprobe_addr() and use it in the kprobe_addr() > > so that it can handle the case that user passed the probe address in > > _text+OFFSET format. > > It works a little... at the very least it still needs > arch_kprobe_on_func_entry() allowing offset 4. > > But looking at this, we've got: > > kprobe_on_func_entry(addr, sym, offset) > _kprobe_addr(addr, sym, offset) > if (sym) > addr = kprobe_lookup_name() > = kallsyms_lookup_name() > arch_adjust_kprobe_addr(addr+offset) > skip_endbr() > kallsyms_loopup_size_offset(addr, ...) > kallsyms_lookup_size_offset(addr, NULL, &offset) > arch_kprobe_on_func_entry(offset) > > Which is _3_ kallsyms lookups and 3 weak/arch hooks.
Yeah.
> > Surely we can make this a little more streamlined? The below seems to > work.
OK, let me check.
> > I think with a little care and testing it should be possible to fold all > the magic of PowerPC's kprobe_lookup_name() into this one hook as well, > meaning we can get rid of kprobe_lookup_name() entirely. Naveen?
Agreed. my previous patch just focused on x86, but powerpc kprobe_lookup_name() must be updated too.
> > This then gets us down to a 1 kallsyms call and 1 arch hook. Hmm? > > --- > arch/powerpc/kernel/kprobes.c | 34 +++++++++++++++--------- > arch/x86/kernel/kprobes/core.c | 17 ++++++++++++ > include/linux/kprobes.h | 3 +- > kernel/kprobes.c | 56 ++++++++++++++++++++++++++++++++++------- > 4 files changed, 87 insertions(+), 23 deletions(-) > > --- a/arch/powerpc/kernel/kprobes.c > +++ b/arch/powerpc/kernel/kprobes.c > @@ -105,6 +105,27 @@ kprobe_opcode_t *kprobe_lookup_name(cons > return addr; > } > > +static bool arch_kprobe_on_func_entry(unsigned long offset) > +{ > +#ifdef PPC64_ELF_ABI_v2 > +#ifdef CONFIG_KPROBES_ON_FTRACE > + return offset <= 16; > +#else > + return offset <= 8; > +#endif > +#else > + return !offset; > +#endif > +} > + > +/* XXX try and fold the magic of kprobe_lookup_name() in this */ > +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset, > + bool *on_func_entry) > +{ > + *on_func_entry = arch_kprobe_on_func_entry(offset); > + return (kprobe_opcode_t *)(addr + offset); > +} > + > void *alloc_insn_page(void) > { > void *page; > @@ -218,19 +239,6 @@ static nokprobe_inline void set_current_ > kcb->kprobe_saved_msr = regs->msr; > } > > -bool arch_kprobe_on_func_entry(unsigned long offset) > -{ > -#ifdef PPC64_ELF_ABI_v2 > -#ifdef CONFIG_KPROBES_ON_FTRACE > - return offset <= 16; > -#else > - return offset <= 8; > -#endif > -#else > - return !offset; > -#endif > -} > - > void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs) > { > ri->ret_addr = (kprobe_opcode_t *)regs->link; > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -52,6 +52,7 @@ > #include <asm/insn.h> > #include <asm/debugreg.h> > #include <asm/set_memory.h> > +#include <asm/ibt.h> > > #include "common.h" > > @@ -301,6 +302,22 @@ static int can_probe(unsigned long paddr > return (addr == paddr); > } > > +/* If the x86 support IBT (ENDBR) it must be skipped. */ > +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset, > + bool *on_func_entry) > +{ > + if (is_endbr(*(u32 *)addr)) { > + *on_func_entry = !offset || offset == 4; > + if (*on_func_entry) > + offset = 4; > + > + } else { > + *on_func_entry = !offset; > + } > + > + return (kprobe_opcode_t *)(addr + offset); > +} > + > /* > * Copy an instruction with recovering modified instruction by kprobes > * and adjust the displacement if the instruction uses the %rip-relative > --- a/include/linux/kprobes.h > +++ b/include/linux/kprobes.h > @@ -265,7 +265,6 @@ extern int arch_init_kprobes(void); > extern void kprobes_inc_nmissed_count(struct kprobe *p); > extern bool arch_within_kprobe_blacklist(unsigned long addr); > extern int arch_populate_kprobe_blacklist(void); > -extern bool arch_kprobe_on_func_entry(unsigned long offset); > extern int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset); > > extern bool within_kprobe_blacklist(unsigned long addr); > @@ -384,6 +383,8 @@ static inline struct kprobe_ctlblk *get_ > } > > kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset); > +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset, bool *on_func_entry); > + > int register_kprobe(struct kprobe *p); > void unregister_kprobe(struct kprobe *p); > int register_kprobes(struct kprobe **kps, int num); > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -1489,24 +1489,63 @@ bool within_kprobe_blacklist(unsigned lo > } > > /* > + * arch_adjust_kprobe_addr - adjust the address > + * @addr: symbol base address > + * @offset: offset within the symbol > + * @on_func_entry: was this @addr+@offset on the function entry > + * > + * Typically returns @addr + @offset, except for special cases where the > + * function might be prefixed by a CFI landing pad, in that case any offset > + * inside the landing pad is mapped to the first 'real' instruction of the > + * symbol. > + * > + * Specifically, for things like IBT/BTI, skip the resp. ENDBR/BTI.C > + * instruction at +0. > + */ > +kprobe_opcode_t *__weak arch_adjust_kprobe_addr(unsigned long addr, > + unsigned long offset, > + bool *on_func_entry) > +{ > + *on_func_entry = !offset; > + return (kprobe_opcode_t *)(addr + offset); > +} > + > +/* > * If 'symbol_name' is specified, look it up and add the 'offset' > * to it. This way, we can specify a relative address to a symbol. > * This returns encoded errors if it fails to look up symbol or invalid > * combination of parameters. > */ > -static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr, > - const char *symbol_name, unsigned int offset) > +static kprobe_opcode_t * > +_kprobe_addr(kprobe_opcode_t *addr, const char *symbol_name, > + unsigned long offset, bool *on_func_entry) > { > if ((symbol_name && addr) || (!symbol_name && !addr)) > goto invalid; > > if (symbol_name) { > + /* > + * Input: @sym + @offset > + * Output: @addr + @offset > + * > + * NOTE: kprobe_lookup_name() does *NOT* fold the offset > + * argument into it's output! > + */ > addr = kprobe_lookup_name(symbol_name, offset);
Hmm, there are 2 issues.
- the 'addr' includes the 'offset' here. - the 'offset' is NOT limited under the symbol size. (e.g. symbol_name = "_text" and @offset points the offset of target symbol from _text)
This means we need to call kallsyms_lookup_size_offset() in this case too.
> if (!addr) > return ERR_PTR(-ENOENT); > + } else { > + /* > + * Input: @addr + @offset > + * Output: @addr' + @offset' > + */ > + if (!kallsyms_lookup_size_offset((unsigned long)addr + offset, > + NULL, &offset)) > + return ERR_PTR(-ENOENT); > + addr = (kprobe_opcode_t *)((unsigned long)addr - offset); > } > > - addr = (kprobe_opcode_t *)(((char *)addr) + offset); > + addr = arch_adjust_kprobe_addr((unsigned long)addr, offset, on_func_entry);
Thus we can ensure the 'offset' here is the real offset from the target function entry.
Thank you,
> if (addr) > return addr; > > @@ -1516,7 +1555,8 @@ static kprobe_opcode_t *_kprobe_addr(kpr > > static kprobe_opcode_t *kprobe_addr(struct kprobe *p) > { > - return _kprobe_addr(p->addr, p->symbol_name, p->offset); > + bool on_func_entry; > + return _kprobe_addr(p->addr, p->symbol_name, p->offset, &on_func_entry); > } > > /* > @@ -2067,15 +2107,13 @@ bool __weak arch_kprobe_on_func_entry(un > */ > int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset) > { > - kprobe_opcode_t *kp_addr = _kprobe_addr(addr, sym, offset); > + bool on_func_entry; > + kprobe_opcode_t *kp_addr = _kprobe_addr(addr, sym, offset, &on_func_entry); > > if (IS_ERR(kp_addr)) > return PTR_ERR(kp_addr); > > - if (!kallsyms_lookup_size_offset((unsigned long)kp_addr, NULL, &offset)) > - return -ENOENT; > - > - if (!arch_kprobe_on_func_entry(offset)) > + if (!on_func_entry) > return -EINVAL; > > return 0;
-- Masami Hiramatsu <mhiramat@kernel.org>
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