From: Andrei Vagin <avagin@xxxxxxxxx>
As it has been discussed on timens RFC, adding a new conditional branch
`if (inside_time_ns)` on VDSO for all processes is undesirable.
Addressing those problems, there are two versions of VDSO's .so:
for host tasks (without any penalty) and for processes inside of time
namespace with clk_to_ns() that subtracts offsets from host's time.
The timens code in vdso looks like this:
if (timens_static_branch_unlikely()) {
clk_to_ns(clk, ts);
}
This static branch is disabled by default. And the code generated consist
of a single atomic 'no-op' instruction, in the straight-line code path.
Enable static branches in the timens vdso: the 'no-op' instruction
gets replaced with a 'jump' instruction to the out-of-line true branch.
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx>
Co-developed-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
---
arch/x86/entry/vdso/vma.c | 30 ++++++++++++++++++++++++------
arch/x86/kernel/jump_label.c | 14 ++++++++++++++
include/linux/jump_label.h | 8 ++++++++
init/Kconfig | 1 +
4 files changed, 47 insertions(+), 6 deletions(-)
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 91cf5a5c8c9e..1a3eb4656eb6 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -15,6 +15,7 @@
#include <linux/cpu.h>
#include <linux/ptrace.h>
#include <linux/time_namespace.h>
+#include <linux/jump_label.h>
#include <asm/pvclock.h>
#include <asm/vgtod.h>
#include <asm/proto.h>
@@ -31,20 +32,37 @@
unsigned int __read_mostly vdso64_enabled = 1;
#endif
-void __init init_vdso_image(struct vdso_image *image)
+#ifdef CONFIG_TIME_NS
+static __init void init_timens(struct vdso_image *image)
{
- BUG_ON(image->size % PAGE_SIZE != 0);
+ struct vdso_jump_entry *entries;
+ unsigned long entries_nr;
+
+ if (WARN_ON(image->jump_table == -1UL))
+ return;
- apply_alternatives((struct alt_instr *)(image->text + image->alt),
- (struct alt_instr *)(image->text + image->alt +
- image->alt_len));
-#ifdef CONFIG_TIME_NS
image->text_timens = vmalloc_32(image->size);
if (WARN_ON(image->text_timens == NULL))
return;
memcpy(image->text_timens, image->text, image->size);
+
+ entries = image->text_timens + image->jump_table;
+ entries_nr = image->jump_table_len / sizeof(struct vdso_jump_entry);
+ apply_vdso_jump_labels(entries, entries_nr);
+}
+#else
+static inline void init_timens(struct vdso_image *image) {}
#endif
+
+void __init init_vdso_image(struct vdso_image *image)
+{
+ BUG_ON(image->size % PAGE_SIZE != 0);
+
+ apply_alternatives((struct alt_instr *)(image->text + image->alt),
+ (struct alt_instr *)(image->text + image->alt +
+ image->alt_len));
+ init_timens(image);
}
struct linux_binprm;
diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 044053235302..7820ac61b688 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -24,6 +24,20 @@ union jump_code_union {
} __attribute__((packed));
};
+__init void apply_vdso_jump_labels(struct vdso_jump_entry *ent, unsigned long nr)
+{
+ while (nr--) {
+ void *code_addr = (void *)ent + ent->code;
+ union jump_code_union jmp;
+
+ jmp.jump = 0xe9; /* JMP rel32 */
+ jmp.offset = ent->target - ent->code - JUMP_LABEL_NOP_SIZE;
+ memcpy(code_addr, &jmp, JUMP_LABEL_NOP_SIZE);
+
+ ent++;
+ }
+}
+
static void bug_at(unsigned char *ip, int line)
{
/*
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 3526c0aee954..bb9d828ee49a 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -125,6 +125,11 @@ struct jump_entry {
long key; // key may be far away from the core kernel under KASLR
};
+struct vdso_jump_entry {
+ u16 code;
+ u16 target;
+};
+
static inline unsigned long jump_entry_code(const struct jump_entry *entry)
{
return (unsigned long)&entry->code + entry->code;
@@ -229,6 +234,9 @@ extern void static_key_enable(struct static_key *key);
extern void static_key_disable(struct static_key *key);
extern void static_key_enable_cpuslocked(struct static_key *key);
extern void static_key_disable_cpuslocked(struct static_key *key);
+extern void apply_vdso_jump_labels(struct vdso_jump_entry *ent,
+ unsigned long nr);
+
/*
* We should be using ATOMIC_INIT() for initializing .enabled, but
diff --git a/init/Kconfig b/init/Kconfig
index 9e40c07da4e1..be8bd41774f6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1072,6 +1072,7 @@ config UTS_NS
config TIME_NS
bool "TIME namespace"
depends on ARCH_HAS_VDSO_TIME_NS
+ depends on JUMP_LABEL
default y
help
In this namespace boottime and monotonic clocks can be set.
--
2.22.0
