[RFC PATCH v2 19/20] arm64: Miscellaneous changes required for enabling livepatch

madvenka
2022-05-24T00:18:45Z

- Create arch/arm64/include/asm/livepatch.h and define
klp_arch_set_pc() and klp_get_ftrace_location() which
are required for livepatch.

- Define TIF_PATCH_PENDING in arch/arm64/include/asm/thread_info.h
for livepatch.

- Check TIF_PATCH_PENDING in do_notify_resume() to patch the
current task for livepatch.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
arch/arm64/include/asm/livepatch.h | 42 ++++++++++++++++++++++++++++
arch/arm64/include/asm/thread_info.h | 4 ++-
arch/arm64/kernel/signal.c | 4 +++
3 files changed, 49 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/include/asm/livepatch.h

diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h
new file mode 100644
index 000000000000..72d7cd86f158
--- /dev/null
+++ b/arch/arm64/include/asm/livepatch.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * livepatch.h - arm64-specific Kernel Live Patching Core
+ */
+#ifndef _ASM_ARM64_LIVEPATCH_H
+#define _ASM_ARM64_LIVEPATCH_H
+
+#include <linux/ftrace.h>
+
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
+{
+ struct pt_regs *regs = ftrace_get_regs(fregs);
+
+ regs->pc = ip;
+}
+
+/*
+ * klp_get_ftrace_location is expected to return the address of the BL to the
+ * relevant ftrace handler in the callsite. The location of this can vary based
+ * on several compilation options.
+ * CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ * - Inserts 2 nops on function entry the second of which is the BL
+ * referenced above. (See ftrace_init_nop() for the callsite sequence)
+ * (this is required by livepatch and must be selected)
+ * CONFIG_ARM64_BTI_KERNEL:
+ * - Inserts a hint #0x22 on function entry if the function is called
+ * indirectly (to satisfy BTI requirements), which is inserted before
+ * the two nops from above.
+ */
+#define klp_get_ftrace_location klp_get_ftrace_location
+static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+ unsigned long addr = faddr + AARCH64_INSN_SIZE;
+
+#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
+ addr = ftrace_location_range(addr, addr + AARCH64_INSN_SIZE);
+#endif
+
+ return addr;
+}
+
+#endif /* _ASM_ARM64_LIVEPATCH_H */
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index e1317b7c4525..a1d8999dbdcc 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -68,6 +68,7 @@ int arch_dup_task_struct(struct task_struct *dst,
#define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */
#define TIF_MTE_ASYNC_FAULT 5 /* MTE Asynchronous Tag Check Fault */
#define TIF_NOTIFY_SIGNAL 6 /* signal notifications exist */
+#define TIF_PATCH_PENDING 7 /* pending live patching update */
#define TIF_SYSCALL_TRACE 8 /* syscall trace active */
#define TIF_SYSCALL_AUDIT 9 /* syscall auditing */
#define TIF_SYSCALL_TRACEPOINT 10 /* syscall tracepoint for ftrace */
@@ -98,11 +99,12 @@ int arch_dup_task_struct(struct task_struct *dst,
#define _TIF_SVE (1 << TIF_SVE)
#define _TIF_MTE_ASYNC_FAULT (1 << TIF_MTE_ASYNC_FAULT)
#define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL)
+#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)

#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
_TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
_TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \
- _TIF_NOTIFY_SIGNAL)
+ _TIF_NOTIFY_SIGNAL | _TIF_PATCH_PENDING)

#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 4a4122ef6f39..cbec9597349f 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -17,6 +17,7 @@
#include <linux/sizes.h>
#include <linux/string.h>
#include <linux/resume_user_mode.h>
+#include <linux/livepatch.h>
#include <linux/ratelimit.h>
#include <linux/syscalls.h>

@@ -938,6 +939,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
(void __user *)NULL, current);
}

+ if (thread_flags & _TIF_PATCH_PENDING)
+ klp_update_patch_state(current);
+
if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
do_signal(regs);

--
2.25.1