hw/sd/sdcard: Fix assertion accessing out-of-range addresses with CMD30

OSS-Fuzz found sending illegal addresses when querying the write
protection bits triggers the assertion added in commit 84816fb63e5
("hw/sd/sdcard: Assert if accessing an illegal group"):

  qemu-fuzz-i386-target-generic-fuzz-sdhci-v3: ../hw/sd/sd.c:824: uint32_t sd_wpbits(SDState *, uint64_t):
  Assertion `wpnum < sd->wpgrps_size' failed.
  #3 0x7f62a8b22c91 in __assert_fail
  #4 0x5569adcec405 in sd_wpbits hw/sd/sd.c:824:9
  #5 0x5569adce5f6d in sd_normal_command hw/sd/sd.c:1389:38
  #6 0x5569adce3870 in sd_do_command hw/sd/sd.c:1737:17
  #7 0x5569adcf1566 in sdbus_do_command hw/sd/core.c:100:16
  #8 0x5569adcfc192 in sdhci_send_command hw/sd/sdhci.c:337:12
  #9 0x5569adcfa3a3 in sdhci_write hw/sd/sdhci.c:1186:9
  #10 0x5569adfb3447 in memory_region_write_accessor softmmu/memory.c:492:5

It is legal for the CMD30 to query for out-of-range addresses.
Such invalid addresses are simply ignored in the response (write
protection bits set to 0).

In commit 84816fb63e5 ("hw/sd/sdcard: Assert if accessing an illegal
group") we misplaced the assertion *before* we test the address is
in range. Move it *after*.

Include the qtest reproducer provided by Alexander Bulekov:

  $ make check-qtest-i386
  ...
  Running test qtest-i386/fuzz-sdcard-test
  qemu-system-i386: ../hw/sd/sd.c:824: sd_wpbits: Assertion `wpnum < sd->wpgrps_size' failed.

Cc: qemu-stable@nongnu.org
Reported-by: OSS-Fuzz (Issue 29225)
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: 84816fb63e5 ("hw/sd/sdcard: Assert if accessing an illegal group")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/495
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210802235524.3417739-3-f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>

2 files changed, 37 insertions, 1 deletions

diff --git a/hw/sd/sd.c b/hw/sd/sd.c
index 707dcc1..bb5dbff 100644
--- a/hw/sd/sd.c
+++ b/hw/sd/sd.c
@@ -821,7 +821,6 @@ static uint32_t sd_wpbits(SDState *sd, uint64_t addr)
     wpnum = sd_addr_to_wpnum(addr);
 
     for (i = 0; i < 32; i++, wpnum++, addr += WPGROUP_SIZE) {
-        assert(wpnum < sd->wpgrps_size);
         if (addr >= sd->size) {
             /*
              * If the addresses of the last groups are outside the valid range,
@@ -829,6 +828,7 @@ static uint32_t sd_wpbits(SDState *sd, uint64_t addr)
              */
             continue;
         }
+        assert(wpnum < sd->wpgrps_size);
         if (test_bit(wpnum, sd->wp_groups)) {
             ret |= (1 << i);
         }
diff --git a/tests/qtest/fuzz-sdcard-test.c b/tests/qtest/fuzz-sdcard-test.c
index 96602ea..ae14305 100644
--- a/tests/qtest/fuzz-sdcard-test.c
+++ b/tests/qtest/fuzz-sdcard-test.c
@@ -52,6 +52,41 @@ static void oss_fuzz_29225(void)
     qtest_quit(s);
 }
 
+/*
+ * https://gitlab.com/qemu-project/qemu/-/issues/495
+ * Used to trigger:
+ *  Assertion `wpnum < sd->wpgrps_size' failed.
+ */
+static void oss_fuzz_36217(void)
+{
+    QTestState *s;
+
+    s = qtest_init(" -display none -m 32 -nodefaults -nographic"
+                   " -device sdhci-pci,sd-spec-version=3 "
+                   "-device sd-card,drive=d0 "
+                   "-drive if=none,index=0,file=null-co://,format=raw,id=d0");
+
+    qtest_outl(s, 0xcf8, 0x80001010);
+    qtest_outl(s, 0xcfc, 0xe0000000);
+    qtest_outl(s, 0xcf8, 0x80001004);
+    qtest_outw(s, 0xcfc, 0x02);
+    qtest_bufwrite(s, 0xe000002c, "\x05", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x37", 0x1);
+    qtest_bufwrite(s, 0xe000000a, "\x01", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x29", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x02", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x03", 0x1);
+    qtest_bufwrite(s, 0xe0000005, "\x01", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x06", 0x1);
+    qtest_bufwrite(s, 0xe000000c, "\x05", 0x1);
+    qtest_bufwrite(s, 0xe000000e, "\x20", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x08", 0x1);
+    qtest_bufwrite(s, 0xe000000b, "\x3d", 0x1);
+    qtest_bufwrite(s, 0xe000000f, "\x1e", 0x1);
+
+    qtest_quit(s);
+}
+
 int main(int argc, char **argv)
 {
     const char *arch = qtest_get_arch();
@@ -60,6 +95,7 @@ int main(int argc, char **argv)
 
    if (strcmp(arch, "i386") == 0) {
         qtest_add_func("fuzz/sdcard/oss_fuzz_29225", oss_fuzz_29225);
+        qtest_add_func("fuzz/sdcard/oss_fuzz_36217", oss_fuzz_36217);
    }
 
    return g_test_run();