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Date: Tue, 1 Mar 2022 11:49:05 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
jpoimboe@...hat.com, andrew.cooper3@...rix.com,
linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
keescook@...omium.org, samitolvanen@...gle.com,
mark.rutland@....com, alyssa.milburn@...el.com, mbenes@...e.cz,
rostedt@...dmis.org, alexei.starovoitov@...il.com,
naveen.n.rao@...ux.vnet.ibm.com
Subject: Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions
On Tue, 1 Mar 2022 00:25:13 +0100
Peter Zijlstra <peterz@...radead.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+@...set 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@...nel.org>
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