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Message-Id: <20220303105440.bd8bb739257a05846b5f2185@kernel.org>
Date: Thu, 3 Mar 2022 10:54:40 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
alexei.starovoitov@...il.com, alyssa.milburn@...el.com,
andrew.cooper3@...rix.com, hjl.tools@...il.com,
joao@...rdrivepizza.com, jpoimboe@...hat.com,
keescook@...omium.org, linux-kernel@...r.kernel.org,
mark.rutland@....com, mbenes@...e.cz,
Masami Hiramatsu <mhiramat@...nel.org>,
ndesaulniers@...gle.com, rostedt@...dmis.org,
samitolvanen@...gle.com, x86@...nel.org
Subject: Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions
On Wed, 02 Mar 2022 21:47:03 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> Peter Zijlstra wrote:
> > --- 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);
> > +}
> > +
>
> With respect to kprobe_lookup_name(), one of the primary motivations there was
> the issue with function descriptors for the previous elf v1 ABI (it likely also
> affects ia64/parisc). I'm thinking it'll be simpler if we have a way to obtain
> function entry point. Something like this:
>
> diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> index 4176c7eca7b5aa..8c57cc5b77f9ae 100644
> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -73,6 +73,12 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
> /* Lookup the address for a symbol. Returns 0 if not found. */
> unsigned long kallsyms_lookup_name(const char *name);
>
> +/* Return function entry point by additionally dereferencing function descriptor */
> +static inline unsigned long kallsyms_lookup_function(const char *name)
> +{
> + return (unsigned long)dereference_symbol_descriptor((void *)kallsyms_lookup_name(name));
> +}
> +
> extern int kallsyms_lookup_size_offset(unsigned long addr,
> unsigned long *symbolsize,
> unsigned long *offset);
> @@ -103,6 +109,11 @@ static inline unsigned long kallsyms_lookup_name(const char *name)
> return 0;
> }
>
> +static inline unsigned long kallsyms_lookup_function(const char *name)
> +{
> + return 0;
> +}
> +
> static inline int kallsyms_lookup_size_offset(unsigned long addr,
> unsigned long *symbolsize,
> unsigned long *offset)
>
>
> With that, we can fold some of the code from kprobe_lookup_name() into
> arch_adjust_kprobe_addr() and remove kprobe_lookup_name(). This should also
> address Masami's concerns with powerpc promoting all probes at function entry
> into a probe at the ftrace location.
Good point, this looks good to me.
And "kallsyms_lookup_entry_address()" will be the preferable name.
Thank you,
>
>
> - Naveen
>
>
> ---
> arch/powerpc/kernel/kprobes.c | 70 +++--------------------------------
> include/linux/kprobes.h | 1 -
> kernel/kprobes.c | 19 ++--------
> kernel/trace/trace_kprobe.c | 2 +-
> 4 files changed, 9 insertions(+), 83 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 7dae0b01abfbd6..46aa2b9e44c27c 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -41,70 +41,6 @@ bool arch_within_kprobe_blacklist(unsigned long addr)
> addr < (unsigned long)__head_end);
> }
>
> -kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
> -{
> - kprobe_opcode_t *addr = NULL;
> -
> -#ifdef PPC64_ELF_ABI_v2
> - /* PPC64 ABIv2 needs local entry point */
> - addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
> - if (addr && !offset) {
> -#ifdef CONFIG_KPROBES_ON_FTRACE
> - unsigned long faddr;
> - /*
> - * Per livepatch.h, ftrace location is always within the first
> - * 16 bytes of a function on powerpc with -mprofile-kernel.
> - */
> - faddr = ftrace_location_range((unsigned long)addr,
> - (unsigned long)addr + 16);
> - if (faddr)
> - addr = (kprobe_opcode_t *)faddr;
> - else
> -#endif
> - addr = (kprobe_opcode_t *)ppc_function_entry(addr);
> - }
> -#elif defined(PPC64_ELF_ABI_v1)
> - /*
> - * 64bit powerpc ABIv1 uses function descriptors:
> - * - Check for the dot variant of the symbol first.
> - * - If that fails, try looking up the symbol provided.
> - *
> - * This ensures we always get to the actual symbol and not
> - * the descriptor.
> - *
> - * Also handle <module:symbol> format.
> - */
> - char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
> - bool dot_appended = false;
> - const char *c;
> - ssize_t ret = 0;
> - int len = 0;
> -
> - if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
> - c++;
> - len = c - name;
> - memcpy(dot_name, name, len);
> - } else
> - c = name;
> -
> - if (*c != '\0' && *c != '.') {
> - dot_name[len++] = '.';
> - dot_appended = true;
> - }
> - ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
> - if (ret > 0)
> - addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
> -
> - /* Fallback to the original non-dot symbol lookup */
> - if (!addr && dot_appended)
> - addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
> -#else
> - addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
> -#endif
> -
> - return addr;
> -}
> -
> static bool arch_kprobe_on_func_entry(unsigned long offset)
> {
> #ifdef PPC64_ELF_ABI_v2
> @@ -118,11 +54,15 @@ static bool arch_kprobe_on_func_entry(unsigned long 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);
> +#ifdef PPC64_ELF_ABI_v2
> + /* Promote probes on the GEP to the LEP */
> + if (!offset)
> + addr = ppc_function_entry((void *)addr);
> +#endif
> return (kprobe_opcode_t *)(addr + offset);
> }
>
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 9c28f7a0ef4268..dad375056ba049 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -382,7 +382,6 @@ static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void)
> return this_cpu_ptr(&kprobe_ctlblk);
> }
>
> -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);
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 8be57fdc19bdc0..066fa644e9dfa3 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -67,12 +67,6 @@ static bool kprobes_all_disarmed;
> static DEFINE_MUTEX(kprobe_mutex);
> static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);
>
> -kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
> - unsigned int __unused)
> -{
> - return ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
> -}
> -
> /*
> * Blacklist -- list of 'struct kprobe_blacklist_entry' to store info where
> * kprobes can not probe.
> @@ -1481,7 +1475,7 @@ bool within_kprobe_blacklist(unsigned long addr)
> if (!p)
> return false;
> *p = '\0';
> - addr = (unsigned long)kprobe_lookup_name(symname, 0);
> + addr = kallsyms_lookup_function(symname);
> if (addr)
> return __within_kprobe_blacklist(addr);
> }
> @@ -1524,14 +1518,7 @@ _kprobe_addr(kprobe_opcode_t *addr, const char *symbol_name,
> 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);
> + addr = (kprobe_opcode_t *)kallsyms_lookup_function(symbol_name);
> if (!addr)
> return ERR_PTR(-ENOENT);
> }
> @@ -2621,7 +2608,7 @@ static int __init init_kprobes(void)
> /* lookup the function address from its name */
> for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
> kretprobe_blacklist[i].addr =
> - kprobe_lookup_name(kretprobe_blacklist[i].name, 0);
> + (void *)kallsyms_lookup_function(kretprobe_blacklist[i].name);
> if (!kretprobe_blacklist[i].addr)
> pr_err("Failed to lookup symbol '%s' for kretprobe blacklist. Maybe the target function is removed or renamed.\n",
> kretprobe_blacklist[i].name);
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 508f14af4f2c7e..a8d01954051e60 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -461,7 +461,7 @@ static bool within_notrace_func(struct trace_kprobe *tk)
> if (!p)
> return true;
> *p = '\0';
> - addr = (unsigned long)kprobe_lookup_name(symname, 0);
> + addr = kallsyms_lookup_function(symname);
> if (addr)
> return __within_notrace_func(addr);
> }
> --
> 2.35.1
>
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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