lib/zlib: unpoison DFLTCC output buffers

The constraints of the DFLTCC inline assembly are not precise: they do not
communicate the size of the output buffers to the compiler, so it cannot
automatically instrument it.

Add the manual kmsan_unpoison_memory() calls for the output buffers. The
logic is the same as in [1].

[1] https://github.com/zlib-ng/zlib-ng/commit/1f5ddcc009ac3511e99fc88736a9e1a6381168c5

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ilya Leoshkevich <[e-mail]>
Reported-by: Alexander Gordeev <[e-mail]>
Reviewed-by: Alexander Potapenko <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Hyeonggon Yoo <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Masami Hiramatsu (Google) <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Steven Rostedt (Google) <[e-mail]>
Cc: Sven Schnelle <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

lib/zlib_dfltcc/dfltcc.h

···
     uint8_t csb[1152];
 };
 
+static_assert(offsetof(struct dfltcc_param_v0, csb) == 384);
 static_assert(sizeof(struct dfltcc_param_v0) == 1536);
 
 #define CVT_CRC32 0

lib/zlib_dfltcc/dfltcc_util.h

···
 #ifndef DFLTCC_UTIL_H
 #define DFLTCC_UTIL_H
 
+#include "dfltcc.h"
+#include <linux/kmsan-checks.h>
 #include <linux/zutil.h>
 
 /*
···
 #define DFLTCC_CMPR 2
 #define DFLTCC_XPND 4
 #define HBT_CIRCULAR (1 << 7)
+#define DFLTCC_FN_MASK ((1 << 7) - 1)
 #define HB_BITS 15
 #define HB_SIZE (1 << HB_BITS)
 
···
 )
 {
     Byte *t2 = op1 ? *op1 : NULL;
+    unsigned char *orig_t2 = t2;
     size_t t3 = len1 ? *len1 : 0;
     const Byte *t4 = op2 ? *op2 : NULL;
     size_t t5 = len2 ? *len2 : 0;
···
                      , [hist] "r" (hist)
                      : "cc", "memory");
     t2 = r2; t3 = r3; t4 = r4; t5 = r5;
+
+    /*
+     * Unpoison the parameter block and the output buffer.
+     * This is a no-op in non-KMSAN builds.
+     */
+    switch (fn & DFLTCC_FN_MASK) {
+    case DFLTCC_QAF:
+        kmsan_unpoison_memory(param, sizeof(struct dfltcc_qaf_param));
+        break;
+    case DFLTCC_GDHT:
+        kmsan_unpoison_memory(param, offsetof(struct dfltcc_param_v0, csb));
+        break;
+    case DFLTCC_CMPR:
+        kmsan_unpoison_memory(param, sizeof(struct dfltcc_param_v0));
+        kmsan_unpoison_memory(
+                orig_t2,
+                t2 - orig_t2 +
+                    (((struct dfltcc_param_v0 *)param)->sbb == 0 ? 0 : 1));
+        break;
+    case DFLTCC_XPND:
+        kmsan_unpoison_memory(param, sizeof(struct dfltcc_param_v0));
+        kmsan_unpoison_memory(orig_t2, t2 - orig_t2);
+        break;
+    }
 
     if (op1)
         *op1 = t2;