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kprobes: Add symbols for kprobe insn pages

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Symbols are needed for tools to describe instruction addresses. Pages
allocated for kprobe's purposes need symbols to be created for them.
Add such symbols to be visible via /proc/kallsyms.

Note: kprobe insn pages are not used if ftrace is configured. To see the
effect of this patch, the kernel must be configured with:

	# CONFIG_FUNCTION_TRACER is not set
	CONFIG_KPROBES=y

and for optimised kprobes:

	CONFIG_OPTPROBES=y

Example on x86:

	# perf probe __schedule
	Added new event:
	  probe:__schedule     (on __schedule)
	# cat /proc/kallsyms | grep '\[__builtin__kprobes\]'
	ffffffffc00d4000 t kprobe_insn_page     [__builtin__kprobes]
	ffffffffc00d6000 t kprobe_optinsn_page  [__builtin__kprobes]

Note: This patch adds "__builtin__kprobes" as a module name in
/proc/kallsyms for symbols for pages allocated for kprobes' purposes, even
though "__builtin__kprobes" is not a module.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lkml.kernel.org/r/20200528080058.20230-1-adrian.hunter@intel.com
This commit is contained in:
Adrian Hunter 2020-05-28 11:00:58 +03:00 • committed by Peter Zijlstra
parent d769811ca9
commit d002b8bc6d
3 changed files with 93 additions and 4 deletions
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37
kernel/kallsyms.c
View file

@ -24,6 +24,7 @@
#include <linux/slab.h>
#include <linux/filter.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/compiler.h>
/*
@ -437,6 +438,7 @@ struct kallsym_iter {
loff_t pos_arch_end;
loff_t pos_mod_end;
loff_t pos_ftrace_mod_end;
loff_t pos_bpf_end;
unsigned long value;
unsigned int nameoff; /* If iterating in core kernel symbols. */
char type;
@ -496,11 +498,33 @@ static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
static int get_ksymbol_bpf(struct kallsym_iter *iter)
{
int ret;
strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
iter->exported = 0;
return bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
&iter->value, &iter->type,
iter->name) < 0 ? 0 : 1;
ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
&iter->value, &iter->type,
iter->name);
if (ret < 0) {
iter->pos_bpf_end = iter->pos;
return 0;
}
return 1;
}
/*
* This uses "__builtin__kprobes" as a module name for symbols for pages
* allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
* module.
*/
static int get_ksymbol_kprobe(struct kallsym_iter *iter)
{
strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
iter->exported = 0;
return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
&iter->value, &iter->type,
iter->name) < 0 ? 0 : 1;
}
/* Returns space to next name. */
@ -527,6 +551,7 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
iter->pos_arch_end = 0;
iter->pos_mod_end = 0;
iter->pos_ftrace_mod_end = 0;
iter->pos_bpf_end = 0;
}
}
@ -551,7 +576,11 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
get_ksymbol_ftrace_mod(iter))
return 1;
return get_ksymbol_bpf(iter);
if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
get_ksymbol_bpf(iter))
return 1;
return get_ksymbol_kprobe(iter);
}
/* Returns false if pos at or past end of file. */