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Date: Wed, 02 Mar 2022 21:47:03 +0530
From: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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
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.
- 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
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