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fuzz: configure a sparse-mem device, by default 

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>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alexander Bulekov 2021-03-15 10:05:11 -04:00 committed by Paolo Bonzini
parent 230376d285
commit 25d309fb0d
1 changed files with 11 additions and 3 deletions
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14
tests/qtest/fuzz/generic_fuzz.c
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@ -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));