tracing: Make trace_seq_putmem_hex() more robust

Currently trace_seq_putmem_hex() can only take as a parameter a pointer
to something that is 8 bytes or less, otherwise it will overflow the
buffer. This is protected by a macro that encompasses the call to
trace_seq_putmem_hex() that has a BUILD_BUG_ON() for the variable before
it is passed in. This is not very robust and if trace_seq_putmem_hex() ever
gets used outside that macro it will cause issues.

Instead of only being able to produce a hex output of memory that is for
a single word, change it to be more robust and allow any size input.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 19 insertions, 8 deletions

diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h
index bf7daf2237ed..80b25b585a70 100644
--- a/kernel/trace/trace_output.h
+++ b/kernel/trace/trace_output.h
@@ -43,7 +43,6 @@ do {							\
 
 #define SEQ_PUT_HEX_FIELD_RET(s, x)                     \
 do {                                                    \
-        BUILD_BUG_ON(sizeof(x) > MAX_MEMHEX_BYTES);     \
         if (!trace_seq_putmem_hex(s, &(x), sizeof(x)))  \
                 return TRACE_TYPE_PARTIAL_LINE;         \
 } while (0)
diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
index 0fabca773e51..88c0f80f0a1f 100644
--- a/kernel/trace/trace_seq.c
+++ b/kernel/trace/trace_seq.c
@@ -291,6 +291,7 @@ int trace_seq_putmem(struct trace_seq *s, const void *mem, unsigned int len)
 }
 EXPORT_SYMBOL_GPL(trace_seq_putmem);
 
+#define MAX_MEMHEX_BYTES        8U
 #define HEX_CHARS               (MAX_MEMHEX_BYTES*2 + 1)
 
 /**
@@ -310,22 +311,33 @@ int trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
 {
         unsigned char hex[HEX_CHARS];
         const unsigned char *data = mem;
+        unsigned int start_len;
         int i, j;
+        int cnt = 0;
 
         if (s->full)
                 return 0;
 
+        while (len) {
+                start_len = min(len, HEX_CHARS - 1);
 #ifdef __BIG_ENDIAN
-        for (i = 0, j = 0; i < len; i++) {
+                for (i = 0, j = 0; i < start_len; i++) {
 #else
-        for (i = len-1, j = 0; i >= 0; i--) {
+                for (i = start_len-1, j = 0; i >= 0; i--) {
 #endif
-                hex[j++] = hex_asc_hi(data[i]);
-                hex[j++] = hex_asc_lo(data[i]);
-        }
-        hex[j++] = ' ';
+                        hex[j++] = hex_asc_hi(data[i]);
+                        hex[j++] = hex_asc_lo(data[i]);
+                }
+                if (WARN_ON_ONCE(j == 0 || j/2 > len))
+                        break;
+
+                /* j increments twice per loop */
+                len -= j / 2;
+                hex[j++] = ' ';
 
-        return trace_seq_putmem(s, hex, j);
+                cnt += trace_seq_putmem(s, hex, j);
+        }
+        return cnt;
 }
 EXPORT_SYMBOL_GPL(trace_seq_putmem_hex);