s390/ftrace: add code replacement sanity checks

Always verify that the to be replaced code matches what we expect to see.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 49 insertions, 46 deletions

diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index b86bb8823f15..3dabcae40e04 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -59,62 +59,65 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
                     unsigned long addr)
 {
-        struct ftrace_insn insn;
-        unsigned short op;
-        void *from, *to;
-        size_t size;
-
-        ftrace_generate_nop_insn(&insn);
-        size = sizeof(insn);
-        from = &insn;
-        to = (void *) rec->ip;
-        if (probe_kernel_read(&op, (void *) rec->ip, sizeof(op)))
+        struct ftrace_insn orig, new, old;
+
+        if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
                 return -EFAULT;
-        /*
-         * If we find a breakpoint instruction, a kprobe has been placed
-         * at the beginning of the function. We write the constant
-         * KPROBE_ON_FTRACE_NOP into the remaining four bytes of the original
-         * instruction so that the kprobes handler can execute a nop, if it
-         * reaches this breakpoint.
-         */
-        if (op == BREAKPOINT_INSTRUCTION) {
-                size -= 2;
-                from += 2;
-                to += 2;
-                insn.disp = KPROBE_ON_FTRACE_NOP;
+        if (addr == MCOUNT_ADDR) {
+                /* Initial code replacement; we expect to see stg r14,8(r15) */
+                orig.opc = 0xe3e0;
+                orig.disp = 0xf0080024;
+                ftrace_generate_nop_insn(&new);
+        } else if (old.opc == BREAKPOINT_INSTRUCTION) {
+                /*
+                 * If we find a breakpoint instruction, a kprobe has been
+                 * placed at the beginning of the function. We write the
+                 * constant KPROBE_ON_FTRACE_NOP into the remaining four
+                 * bytes of the original instruction so that the kprobes
+                 * handler can execute a nop, if it reaches this breakpoint.
+                 */
+                new.opc = orig.opc = BREAKPOINT_INSTRUCTION;
+                orig.disp = KPROBE_ON_FTRACE_CALL;
+                new.disp = KPROBE_ON_FTRACE_NOP;
+        } else {
+                /* Replace ftrace call with a nop. */
+                ftrace_generate_call_insn(&orig, rec->ip);
+                ftrace_generate_nop_insn(&new);
         }
-        if (probe_kernel_write(to, from, size))
+        /* Verify that the to be replaced code matches what we expect. */
+        if (memcmp(&orig, &old, sizeof(old)))
+                return -EINVAL;
+        if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))
                 return -EPERM;
         return 0;
 }
 
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
-        struct ftrace_insn insn;
-        unsigned short op;
-        void *from, *to;
-        size_t size;
-
-        ftrace_generate_call_insn(&insn, rec->ip);
-        size = sizeof(insn);
-        from = &insn;
-        to = (void *) rec->ip;
-        if (probe_kernel_read(&op, (void *) rec->ip, sizeof(op)))
+        struct ftrace_insn orig, new, old;
+
+        if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
                 return -EFAULT;
-        /*
-         * If we find a breakpoint instruction, a kprobe has been placed
-         * at the beginning of the function. We write the constant
-         * KPROBE_ON_FTRACE_CALL into the remaining four bytes of the original
-         * instruction so that the kprobes handler can execute a brasl if it
-         * reaches this breakpoint.
-         */
-        if (op == BREAKPOINT_INSTRUCTION) {
-                size -= 2;
-                from += 2;
-                to += 2;
-                insn.disp = KPROBE_ON_FTRACE_CALL;
+        if (old.opc == BREAKPOINT_INSTRUCTION) {
+                /*
+                 * If we find a breakpoint instruction, a kprobe has been
+                 * placed at the beginning of the function. We write the
+                 * constant KPROBE_ON_FTRACE_CALL into the remaining four
+                 * bytes of the original instruction so that the kprobes
+                 * handler can execute a brasl if it reaches this breakpoint.
+                 */
+                new.opc = orig.opc = BREAKPOINT_INSTRUCTION;
+                orig.disp = KPROBE_ON_FTRACE_NOP;
+                new.disp = KPROBE_ON_FTRACE_CALL;
+        } else {
+                /* Replace nop with an ftrace call. */
+                ftrace_generate_nop_insn(&orig);
+                ftrace_generate_call_insn(&new, rec->ip);
         }
-        if (probe_kernel_write(to, from, size))
+        /* Verify that the to be replaced code matches what we expect. */
+        if (memcmp(&orig, &old, sizeof(old)))
+                return -EINVAL;
+        if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))
                 return -EPERM;
         return 0;
 }