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From: Alexander Bulekov <alxndr@bu.edu>
To: qemu-devel@nongnu.org
Cc: Laurent Vivier <lvivier@redhat.com>,
	Thomas Huth <thuth@redhat.com>,
	darren.kenny@oracle.com, f4bug@amsat.org,
	Alexander Bulekov <alxndr@bu.edu>,
	bsd@redhat.com, stefanha@redhat.com, pbonzini@redhat.com
Subject: [PATCH v2 2/3] fuzz: configure a sparse-mem device, by default
Date: Sat, 13 Mar 2021 18:18:58 -0500
Message-ID: <20210313231859.941263-3-alxndr@bu.edu> (raw)
In-Reply-To: <20210313231859.941263-1-alxndr@bu.edu>

The generic-fuzzer often provides randomized DMA addresses to
virtual-devices. For a 64-bit address-space, the chance of these
randomized addresses coinciding with RAM regions, is fairly small. Even
though the fuzzer's instrumentation eventually finds valid addresses,
this can take some-time, and slows-down fuzzing progress (especially,
when multiple DMA buffers are involved). To work around this, create
"fake" sparse-memory that spans all of the 64-bit address-space. Adjust
the DMA call-back to populate this sparse memory, correspondingly

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 tests/qtest/fuzz/generic_fuzz.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c
index 387ae2020a..b5fe27aae1 100644
--- a/tests/qtest/fuzz/generic_fuzz.c
+++ b/tests/qtest/fuzz/generic_fuzz.c
@@ -28,6 +28,7 @@
 #include "hw/pci/pci.h"
 #include "hw/boards.h"
 #include "generic_fuzz_configs.h"
+#include "hw/mem/sparse-mem.h"
 
 /*
  * SEPARATOR is used to separate "operations" in the fuzz input
@@ -64,6 +65,8 @@ static useconds_t timeout = DEFAULT_TIMEOUT_US;
 
 static bool qtest_log_enabled;
 
+MemoryRegion *sparse_mem_mr;
+
 /*
  * A pattern used to populate a DMA region or perform a memwrite. This is
  * useful for e.g. populating tables of unique addresses.
@@ -191,8 +194,7 @@ void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr)
      */
     if (dma_patterns->len == 0
         || len == 0
-        || mr != current_machine->ram
-        || addr > current_machine->ram_size) {
+        || (mr != current_machine->ram && mr != sparse_mem_mr)) {
         return;
     }
 
@@ -238,7 +240,7 @@ void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr)
                                       MEMTXATTRS_UNSPECIFIED);
 
         if (!(memory_region_is_ram(mr1) ||
-              memory_region_is_romd(mr1))) {
+              memory_region_is_romd(mr1)) && mr1 != sparse_mem_mr) {
             l = memory_access_size(mr1, l, addr1);
         } else {
             /* ROM/RAM case */
@@ -814,6 +816,12 @@ static void generic_pre_fuzz(QTestState *s)
     }
     qts_global = s;
 
+    /*
+     * Create a special device that we can use to back DMA buffers at very
+     * high memory addresses
+     */
+    sparse_mem_mr = sparse_mem_init(0, UINT64_MAX);
+
     dma_regions = g_array_new(false, false, sizeof(address_range));
     dma_patterns = g_array_new(false, false, sizeof(pattern));
 
-- 
2.28.0



  parent reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-13 23:18 [PATCH v2 0/3] fuzz: Add a sparse-memory device to accelerate fuzzing Alexander Bulekov
2021-03-13 23:18 ` [PATCH v2 1/3] memory: add a sparse memory device for fuzzing Alexander Bulekov
2021-03-14 23:14   ` Alexander Bulekov
2021-03-15 12:09   ` Darren Kenny
2021-03-15 13:52     ` Alexander Bulekov
2021-03-13 23:18 ` Alexander Bulekov [this message]
2021-03-15 12:12   ` [PATCH v2 2/3] fuzz: configure a sparse-mem device, by default Darren Kenny
2021-03-13 23:18 ` [PATCH v2 3/3] fuzz: move some DMA hooks Alexander Bulekov
2021-03-15 12:12   ` Darren Kenny

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