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Subject[PATCH V4 2/3] kallsyms, x86: Export addresses of PTI entry trampolines
Date
From: Alexander Shishkin <alexander.shishkin@linux.intel.com>

Currently, the addresses of PTI entry trampolines are not exported to user
space. Kernel profiling tools need these addresses to identify the kernel
code, so add a symbol and address for each CPU's PTI entry trampoline.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
---
arch/x86/mm/cpu_entry_area.c | 23 +++++++++++++++++++++++
kernel/kallsyms.c | 28 +++++++++++++++++++++++++++-
2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index b45f5aaefd74..fab49fd5190f 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -2,6 +2,7 @@

#include <linux/spinlock.h>
#include <linux/percpu.h>
+#include <linux/kallsyms.h>

#include <asm/cpu_entry_area.h>
#include <asm/pgtable.h>
@@ -150,6 +151,28 @@ static void __init setup_cpu_entry_area(int cpu)
percpu_setup_debug_store(cpu);
}

+#ifdef CONFIG_X86_64
+int arch_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+ char *name)
+{
+ unsigned int cpu, ncpu = 0;
+
+ if (symnum >= num_possible_cpus())
+ return -EINVAL;
+
+ for_each_possible_cpu(cpu) {
+ if (ncpu++ >= symnum)
+ break;
+ }
+
+ *value = (unsigned long)&get_cpu_entry_area(cpu)->entry_trampoline;
+ *type = 't';
+ strlcpy(name, "__entry_SYSCALL_64_trampoline", KSYM_NAME_LEN);
+
+ return 0;
+}
+#endif
+
static __init void setup_cpu_entry_area_ptes(void)
{
#ifdef CONFIG_X86_32
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index aa31aa07f2ef..02a0b01380d8 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -432,6 +432,7 @@ int sprint_backtrace(char *buffer, unsigned long address)
/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
struct kallsym_iter {
loff_t pos;
+ loff_t pos_arch_end;
loff_t pos_mod_end;
loff_t pos_ftrace_mod_end;
unsigned long value;
@@ -443,9 +444,29 @@ struct kallsym_iter {
int show_value;
};

+int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
+ char *type, char *name)
+{
+ return -EINVAL;
+}
+
+static int get_ksymbol_arch(struct kallsym_iter *iter)
+{
+ int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
+ &iter->value, &iter->type,
+ iter->name);
+
+ if (ret < 0) {
+ iter->pos_arch_end = iter->pos;
+ return 0;
+ }
+
+ return 1;
+}
+
static int get_ksymbol_mod(struct kallsym_iter *iter)
{
- int ret = module_get_kallsym(iter->pos - kallsyms_num_syms,
+ int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
&iter->value, &iter->type,
iter->name, iter->module_name,
&iter->exported);
@@ -501,6 +522,7 @@ static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
iter->nameoff = get_symbol_offset(new_pos);
iter->pos = new_pos;
if (new_pos == 0) {
+ iter->pos_arch_end = 0;
iter->pos_mod_end = 0;
iter->pos_ftrace_mod_end = 0;
}
@@ -515,6 +537,10 @@ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
{
iter->pos = pos;

+ if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
+ get_ksymbol_arch(iter))
+ return 1;
+
if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
get_ksymbol_mod(iter))
return 1;
--
1.9.1
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