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Subject[PATCH v6 2/7] arm64: introduce interfaces to hotpatch kernel and module code
Date
Introduce three interfaces to patch kernel and module code:
aarch64_insn_patch_text_nosync():
patch code without synchronization, it's caller's responsibility
to synchronize all CPUs if needed.
aarch64_insn_patch_text_sync():
patch code and always synchronize with stop_machine()
aarch64_insn_patch_text():
patch code and synchronize with stop_machine() if needed

Signed-off-by: Jiang Liu <liuj97@gmail.com>
---
arch/arm64/include/asm/insn.h | 10 +++-
arch/arm64/kernel/insn.c | 117 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 126 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index 1bdc44c..bf8085f 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -18,6 +18,9 @@
#define __ASM_INSN_H
#include <linux/types.h>

+/* A64 instructions are always 32 bits. */
+#define AARCH64_INSN_SIZE 4
+
/*
* ARM Architecture Reference Manual for ARMv8 Profile-A, Issue A.a
* Section C3.1 "A64 instruction index by encoding":
@@ -70,8 +73,13 @@ __AARCH64_INSN_FUNCS(hint, 0xFFFFF01F, 0xD503201F)

bool aarch64_insn_is_nop(u32 insn);

+int aarch64_insn_read(void *addr, u32 *insnp);
+int aarch64_insn_write(void *addr, u32 insn);
enum aarch64_insn_encoding_class aarch64_get_insn_class(u32 insn);
-
bool aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn);

+int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
+int aarch64_insn_patch_text_sync(void *addrs[], u32 insns[], int cnt);
+int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
+
#endif /* __ASM_INSN_H */
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index 56a2498..c1b002a8 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -16,6 +16,10 @@
*/
#include <linux/compiler.h>
#include <linux/kernel.h>
+#include <linux/smp.h>
+#include <linux/stop_machine.h>
+#include <linux/uaccess.h>
+#include <asm/cacheflush.h>
#include <asm/insn.h>

static int aarch64_insn_encoding_class[] = {
@@ -60,6 +64,28 @@ bool __kprobes aarch64_insn_is_nop(u32 insn)
}
}

+/*
+ * In ARMv8-A, A64 instructions have a fixed length of 32 bits and are always
+ * little-endian.
+ */
+int __kprobes aarch64_insn_read(void *addr, u32 *insnp)
+{
+ int ret;
+ u32 val;
+
+ ret = probe_kernel_read(&val, addr, AARCH64_INSN_SIZE);
+ if (!ret)
+ *insnp = le32_to_cpu(val);
+
+ return ret;
+}
+
+int __kprobes aarch64_insn_write(void *addr, u32 insn)
+{
+ insn = cpu_to_le32(insn);
+ return probe_kernel_write(addr, &insn, AARCH64_INSN_SIZE);
+}
+
static bool __kprobes __aarch64_insn_hotpatch_safe(u32 insn)
{
if (aarch64_get_insn_class(insn) != AARCH64_INSN_CLS_BR_SYS)
@@ -89,3 +115,94 @@ bool __kprobes aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn)
return __aarch64_insn_hotpatch_safe(old_insn) &&
__aarch64_insn_hotpatch_safe(new_insn);
}
+
+int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
+{
+ u32 *tp = addr;
+ int ret;
+
+ /* A64 instructions must be word aligned */
+ if ((uintptr_t)tp & 0x3)
+ return -EINVAL;
+
+ ret = aarch64_insn_write(tp, insn);
+ if (ret == 0)
+ flush_icache_range((uintptr_t)tp,
+ (uintptr_t)tp + AARCH64_INSN_SIZE);
+
+ return ret;
+}
+
+struct aarch64_insn_patch {
+ void **text_addrs;
+ u32 *new_insns;
+ int insn_cnt;
+ atomic_t cpu_count;
+};
+
+static int __kprobes aarch64_insn_patch_text_cb(void *arg)
+{
+ int i, ret = 0;
+ struct aarch64_insn_patch *pp = arg;
+
+ /* The first CPU becomes master */
+ if (atomic_inc_return(&pp->cpu_count) == 1) {
+ for (i = 0; ret == 0 && i < pp->insn_cnt; i++)
+ ret = aarch64_insn_patch_text_nosync(pp->text_addrs[i],
+ pp->new_insns[i]);
+ /* Make sure changes are visible to other CPUs and let them continue */
+ smp_wmb();
+ atomic_set(&pp->cpu_count, -1);
+ } else {
+ while (atomic_read(&pp->cpu_count) != -1)
+ cpu_relax();
+ smp_rmb();
+ isb();
+ }
+
+ return ret;
+}
+
+int __kprobes aarch64_insn_patch_text_sync(void *addrs[], u32 insns[], int cnt)
+{
+ struct aarch64_insn_patch patch = {
+ .text_addrs = addrs,
+ .new_insns = insns,
+ .insn_cnt = cnt,
+ .cpu_count = ATOMIC_INIT(0),
+ };
+
+ if (cnt <= 0)
+ return -EINVAL;
+
+ return stop_machine(aarch64_insn_patch_text_cb, &patch,
+ cpu_online_mask);
+}
+
+int __kprobes aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt)
+{
+ int ret;
+ u32 insn;
+
+ /* Unsafe to patch multiple instructions without synchronizaiton */
+ if (cnt == 1) {
+ ret = aarch64_insn_read(addrs[0], &insn);
+ if (ret)
+ return ret;
+
+ if (aarch64_insn_hotpatch_safe(insn, insns[0])) {
+ /*
+ * ARMv8 architecture doesn't guarantee all CPUs see
+ * the new instruction after returning from function
+ * aarch64_insn_patch_text_nosync(). So send IPIs to
+ * all other CPUs to achieve instruction
+ * synchronization.
+ */
+ ret = aarch64_insn_patch_text_nosync(addrs[0], insns[0]);
+ kick_all_cpus_sync();
+ return ret;
+ }
+ }
+
+ return aarch64_insn_patch_text_sync(addrs, insns, cnt);
+}
--
1.8.1.2


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