| Message ID | 20200819061110.1320568-5-alxndr@bu.edu |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
On 200903 0943, Darren Kenny wrote: > On Wednesday, 2020-08-19 at 02:10:59 -04, Alexander Bulekov wrote: > > When a virtual-device tries to access some buffer in memory over DMA, we > > add call-backs into the fuzzer(next commit). The fuzzer checks verifies > > that the DMA request maps to a physical RAM address and fills the memory > > with fuzzer-provided data. The patterns that we use to fill this memory > > are specified using add_dma_pattern and clear_dma_patterns operations. > > > > Signed-off-by: Alexander Bulekov <alxndr@bu.edu> > > --- > > tests/qtest/fuzz/general_fuzz.c | 178 ++++++++++++++++++++++++++++++++ > > 1 file changed, 178 insertions(+) > > > > diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c > > index 17b572a439..36d41acea0 100644 > > --- a/tests/qtest/fuzz/general_fuzz.c > > +++ b/tests/qtest/fuzz/general_fuzz.c > > @@ -25,6 +25,8 @@ > > #include "exec/address-spaces.h" > > #include "hw/qdev-core.h" > > #include "hw/pci/pci.h" > > +#include "hw/boards.h" > > +#include "exec/memory-internal.h" > > > > /* > > * SEPARATOR is used to separate "operations" in the fuzz input > > @@ -38,12 +40,16 @@ enum cmds{ > > OP_WRITE, > > OP_PCI_READ, > > OP_PCI_WRITE, > > + OP_ADD_DMA_PATTERN, > > + OP_CLEAR_DMA_PATTERNS, > > OP_CLOCK_STEP, > > }; > > > > #define DEFAULT_TIMEOUT_US 100000 > > #define USEC_IN_SEC 100000000 > > > > +#define MAX_DMA_FILL_SIZE 0x10000 > > + > > #define PCI_HOST_BRIDGE_CFG 0xcf8 > > #define PCI_HOST_BRIDGE_DATA 0xcfc > > > > @@ -53,6 +59,24 @@ typedef struct { > > } address_range; > > > > static useconds_t timeout = 100000; > > +/* > > + * A pattern used to populate a DMA region or perform a memwrite. This is > > + * useful for e.g. populating tables of unique addresses. > > + * Example {.index = 1; .stride = 2; .len = 3; .data = "\x00\x01\x02"} > > + * Renders as: 00 01 02 00 03 03 00 05 03 00 07 03 ... > > TYPO: I think this wrong, and that the last digit should be 02 not 03 in > each group. > Ah thanks for catching that. > > + */ > > +typedef struct { > > + uint8_t index; /* Index of a byte to increment by stride */ > > + uint8_t stride; /* Increment each index'th byte by this amount */ > > + size_t len; > > + const uint8_t *data; > > +} pattern; > > + > > +/* Avoid filling the same DMA region between MMIO/PIO commands ? */ > > +static bool avoid_double_fetches; > > + > > +static QTestState *qts_global; /* Need a global for the DMA callback */ > > + > > /* > > * List of memory regions that are children of QOM objects specified by the > > * user for fuzzing. > > @@ -60,6 +84,116 @@ static useconds_t timeout = 100000; > > static GPtrArray *fuzzable_memoryregions; > > static GPtrArray *fuzzable_pci_devices; > > > > +/* > > + * List of dma regions populated since the last fuzzing command. Used to ensure > > + * that we only write to each DMA address once, to avoid race conditions when > > + * building reproducers. > > + */ > > +static GArray *dma_regions; > > + > > +static GArray *dma_patterns; > > +static int dma_pattern_index; > > + > > +void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr, bool is_write); > > + > > +/* > > + * Allocate a block of memory and populate it with a pattern. > > + */ > > +static void *pattern_alloc(pattern p, size_t len) > > +{ > > + int i; > > + uint8_t *buf = g_malloc(len); > > + uint8_t sum = 0; > > + > > + for (i = 0; i < len; ++i) { > > + buf[i] = p.data[i % p.len]; > > + if ((i % p.len) == p.index) { > > + buf[i] += sum; > > + sum += p.stride; > > + } > > + } > > + return buf; > > +} > > + > > +/* > > + * Call-back for functions that perform DMA reads from guest memory. Confirm > > + * that the region has not already been populated since the last loop in > > + * general_fuzz(), avoiding potential race-conditions, which we don't have > > + * a good way for reproducing right now. > > + */ > > +void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr, bool is_write) > > +{ > > + /* Are we in the general-fuzzer or are we using another fuzz-target? */ > > + if (!qts_global) { > > + return; > > + } > > + > > + /* > > + * Return immediately if: > > + * - We have no DMA patterns defined > > + * - The length of the DMA read request is zero > > + * - The DMA read is hitting an MR other than the machine's main RAM > > + * - The DMA request is not a read (what happens for a address_space_map > > + * with is_write=True? Can the device use the same pointer to do reads?) > > + * - The DMA request hits past the bounds of our RAM > > + */ > > + if (dma_patterns->len == 0 > > + || len == 0 > > + || (mr != MACHINE(qdev_get_machine())->ram && !(mr->ops == &unassigned_mem_ops)) > > + || is_write > > + || addr > current_machine->ram_size) { > > + return; > > + } > > + > > + /* > > + * If we overlap with any existing dma_regions, split the range and only > > + * populate the non-overlapping parts. > > + */ > > + for (int i = 0; i < dma_regions->len && avoid_double_fetches; ++i) { > > + address_range region = g_array_index(dma_regions, address_range, i); > > NIT: Can be slightly more expensive to declare a variable on each > iteration, but also tends to be cleaner not to do this. Ok, I'll fix that. > > + if (addr < region.addr + region.len && addr + len > region.addr) { > > + if (addr < region.addr) { > > + fuzz_dma_read_cb(addr, region.addr - addr, mr, is_write); > > + } > > + if (addr + len > region.addr + region.len) { > > + fuzz_dma_read_cb(region.addr + region.len, > > + addr + len - (region.addr + region.len), mr, is_write); > > + } > > + return; > > + } > > + } > > + > > + /* Cap the length of the DMA access to something reasonable */ > > + len = MIN(len, MAX_DMA_FILL_SIZE); > > + > > + address_range ar = {addr, len}; > > + g_array_append_val(dma_regions, ar); > > + pattern p = g_array_index(dma_patterns, pattern, dma_pattern_index); > > + void *buf = pattern_alloc(p, ar.len); > > + if (getenv("QTEST_LOG")) { > > NIT: It might be cleaner to put any testing of env vars in to > the code in general_fuzz() where most others are being tested, and > instead set a static global boolean which can be used here instead. > Depending on how many times this is called, it may also be slightly > faster since getenv() has to search an array of strings, etc. to get the > value. True. I think the env-variables, in-general, need to be handled/documented in some consistent location. > > + /* > > + * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix the log > > + * that will be written by qtest.c with a DMA tag, so we can reorder > > + * the resulting QTest trace so the DMA fills precede the last PIO/MMIO > > + * command. > > + */ > > + fprintf(stderr, "[DMA] "); > > + fflush(stderr); > > + qtest_memwrite(qts_global, ar.addr, buf, ar.len); > > + } else { > > + /* > > + * Populate the region using address_space_write_rom to avoid writing to > > + * any IO MemoryRegions > > + */ > > + address_space_write_rom(first_cpu->as, ar.addr, MEMTXATTRS_UNSPECIFIED, > > + buf, ar.len); > > + } > > + free(buf); > > NIT: For consistency, this probably should be a g_free(), since the memory > was allocated using g_malloc(). > Oops - I'll fix that. > > + > > + /* Increment the index of the pattern for the next DMA access */ > > + dma_pattern_index = (dma_pattern_index + 1) % dma_patterns->len; > > +} > > + > > /* > > * Here we want to convert a fuzzer-provided [io-region-index, offset] to > > * a physical address. To do this, we iterate over all of the matched > > @@ -350,6 +484,35 @@ static void op_pci_write(QTestState *s, const unsigned char * data, size_t len) > > } > > } > > > > +static void op_add_dma_pattern(QTestState *s, > > + const unsigned char *data, size_t len) > > +{ > > + struct { > > + /* > > + * index and stride can be used to increment the index-th byte of the > > + * pattern by the value stride, for each loop of the pattern. > > + */ > > + uint8_t index; > > + uint8_t stride; > > + } a; > > + > > + if (len < sizeof(a) + 1) { > > + return; > > + } > > + memcpy(&a, data, sizeof(a)); > > + pattern p = {a.index, a.stride, len - sizeof(a), data + sizeof(a)}; > > + p.index = a.index % p.len; > > + g_array_append_val(dma_patterns, p); > > + return; > > +} > > + > > +static void op_clear_dma_patterns(QTestState *s, > > + const unsigned char *data, size_t len) > > +{ > > + g_array_set_size(dma_patterns, 0); > > + dma_pattern_index = 0; > > +} > > + > > static void op_clock_step(QTestState *s, const unsigned char *data, size_t len) > > { > > qtest_clock_step_next(s); > > @@ -396,6 +559,8 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size) > > [OP_WRITE] = op_write, > > [OP_PCI_READ] = op_pci_read, > > [OP_PCI_WRITE] = op_pci_write, > > + [OP_ADD_DMA_PATTERN] = op_add_dma_pattern, > > + [OP_CLEAR_DMA_PATTERNS] = op_clear_dma_patterns, > > [OP_CLOCK_STEP] = op_clock_step, > > }; > > const unsigned char *cmd = Data; > > @@ -425,6 +590,8 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size) > > setitimer(ITIMER_VIRTUAL, &timer, NULL); > > } > > > > + op_clear_dma_patterns(s, NULL, 0); > > + > > while (cmd && Size) { > > /* Get the length until the next command or end of input */ > > nextcmd = memmem(cmd, Size, SEPARATOR, strlen(SEPARATOR)); > > @@ -441,6 +608,7 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size) > > /* Advance to the next command */ > > cmd = nextcmd ? nextcmd + sizeof(SEPARATOR) - 1 : nextcmd; > > Size = Size - (cmd_len + sizeof(SEPARATOR) - 1); > > + g_array_set_size(dma_regions, 0); > > } > > _Exit(0); > > } else { > > @@ -455,6 +623,9 @@ static void usage(void) > > printf("QEMU_FUZZ_ARGS= the command line arguments passed to qemu\n"); > > printf("QEMU_FUZZ_OBJECTS= " > > "a space separated list of QOM type names for objects to fuzz\n"); > > + printf("Optionally: QEMU_AVOID_DOUBLE_FETCH= " > > + "Try to avoid racy DMA double fetch bugs? %d by default\n", > > + avoid_double_fetches); > > printf("Optionally: QEMU_FUZZ_TIMEOUT= Specify a custom timeout (us). " > > "0 to disable. %d by default\n", timeout); > > exit(0); > > @@ -522,9 +693,16 @@ static void general_pre_fuzz(QTestState *s) > > if (!getenv("QEMU_FUZZ_OBJECTS")) { > > usage(); > > } > > + if (getenv("QEMU_AVOID_DOUBLE_FETCH")) { > > + avoid_double_fetches = 1; > > + } > > if (getenv("QEMU_FUZZ_TIMEOUT")) { > > timeout = g_ascii_strtoll(getenv("QEMU_FUZZ_TIMEOUT"), NULL, 0); > > } > > + qts_global = s; > > + > > + dma_regions = g_array_new(false, false, sizeof(address_range)); > > + dma_patterns = g_array_new(false, false, sizeof(pattern)); > > > > fuzzable_memoryregions = g_ptr_array_new(); > > fuzzable_pci_devices = g_ptr_array_new(); > > Since mostly nits and typos: > > Reviewed-by: Darren Kenny <darren.kenny@oracle.com> > > Thanks, > > Darren.
diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c index 17b572a439..36d41acea0 100644 --- a/tests/qtest/fuzz/general_fuzz.c +++ b/tests/qtest/fuzz/general_fuzz.c @@ -25,6 +25,8 @@ #include "exec/address-spaces.h" #include "hw/qdev-core.h" #include "hw/pci/pci.h" +#include "hw/boards.h" +#include "exec/memory-internal.h" /* * SEPARATOR is used to separate "operations" in the fuzz input @@ -38,12 +40,16 @@ enum cmds{ OP_WRITE, OP_PCI_READ, OP_PCI_WRITE, + OP_ADD_DMA_PATTERN, + OP_CLEAR_DMA_PATTERNS, OP_CLOCK_STEP, }; #define DEFAULT_TIMEOUT_US 100000 #define USEC_IN_SEC 100000000 +#define MAX_DMA_FILL_SIZE 0x10000 + #define PCI_HOST_BRIDGE_CFG 0xcf8 #define PCI_HOST_BRIDGE_DATA 0xcfc @@ -53,6 +59,24 @@ typedef struct { } address_range; static useconds_t timeout = 100000; +/* + * A pattern used to populate a DMA region or perform a memwrite. This is + * useful for e.g. populating tables of unique addresses. + * Example {.index = 1; .stride = 2; .len = 3; .data = "\x00\x01\x02"} + * Renders as: 00 01 02 00 03 03 00 05 03 00 07 03 ... + */ +typedef struct { + uint8_t index; /* Index of a byte to increment by stride */ + uint8_t stride; /* Increment each index'th byte by this amount */ + size_t len; + const uint8_t *data; +} pattern; + +/* Avoid filling the same DMA region between MMIO/PIO commands ? */ +static bool avoid_double_fetches; + +static QTestState *qts_global; /* Need a global for the DMA callback */ + /* * List of memory regions that are children of QOM objects specified by the * user for fuzzing. @@ -60,6 +84,116 @@ static useconds_t timeout = 100000; static GPtrArray *fuzzable_memoryregions; static GPtrArray *fuzzable_pci_devices; +/* + * List of dma regions populated since the last fuzzing command. Used to ensure + * that we only write to each DMA address once, to avoid race conditions when + * building reproducers. + */ +static GArray *dma_regions; + +static GArray *dma_patterns; +static int dma_pattern_index; + +void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr, bool is_write); + +/* + * Allocate a block of memory and populate it with a pattern. + */ +static void *pattern_alloc(pattern p, size_t len) +{ + int i; + uint8_t *buf = g_malloc(len); + uint8_t sum = 0; + + for (i = 0; i < len; ++i) { + buf[i] = p.data[i % p.len]; + if ((i % p.len) == p.index) { + buf[i] += sum; + sum += p.stride; + } + } + return buf; +} + +/* + * Call-back for functions that perform DMA reads from guest memory. Confirm + * that the region has not already been populated since the last loop in + * general_fuzz(), avoiding potential race-conditions, which we don't have + * a good way for reproducing right now. + */ +void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr, bool is_write) +{ + /* Are we in the general-fuzzer or are we using another fuzz-target? */ + if (!qts_global) { + return; + } + + /* + * Return immediately if: + * - We have no DMA patterns defined + * - The length of the DMA read request is zero + * - The DMA read is hitting an MR other than the machine's main RAM + * - The DMA request is not a read (what happens for a address_space_map + * with is_write=True? Can the device use the same pointer to do reads?) + * - The DMA request hits past the bounds of our RAM + */ + if (dma_patterns->len == 0 + || len == 0 + || (mr != MACHINE(qdev_get_machine())->ram && !(mr->ops == &unassigned_mem_ops)) + || is_write + || addr > current_machine->ram_size) { + return; + } + + /* + * If we overlap with any existing dma_regions, split the range and only + * populate the non-overlapping parts. + */ + for (int i = 0; i < dma_regions->len && avoid_double_fetches; ++i) { + address_range region = g_array_index(dma_regions, address_range, i); + if (addr < region.addr + region.len && addr + len > region.addr) { + if (addr < region.addr) { + fuzz_dma_read_cb(addr, region.addr - addr, mr, is_write); + } + if (addr + len > region.addr + region.len) { + fuzz_dma_read_cb(region.addr + region.len, + addr + len - (region.addr + region.len), mr, is_write); + } + return; + } + } + + /* Cap the length of the DMA access to something reasonable */ + len = MIN(len, MAX_DMA_FILL_SIZE); + + address_range ar = {addr, len}; + g_array_append_val(dma_regions, ar); + pattern p = g_array_index(dma_patterns, pattern, dma_pattern_index); + void *buf = pattern_alloc(p, ar.len); + if (getenv("QTEST_LOG")) { + /* + * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix the log + * that will be written by qtest.c with a DMA tag, so we can reorder + * the resulting QTest trace so the DMA fills precede the last PIO/MMIO + * command. + */ + fprintf(stderr, "[DMA] "); + fflush(stderr); + qtest_memwrite(qts_global, ar.addr, buf, ar.len); + } else { + /* + * Populate the region using address_space_write_rom to avoid writing to + * any IO MemoryRegions + */ + address_space_write_rom(first_cpu->as, ar.addr, MEMTXATTRS_UNSPECIFIED, + buf, ar.len); + } + free(buf); + + /* Increment the index of the pattern for the next DMA access */ + dma_pattern_index = (dma_pattern_index + 1) % dma_patterns->len; +} + /* * Here we want to convert a fuzzer-provided [io-region-index, offset] to * a physical address. To do this, we iterate over all of the matched @@ -350,6 +484,35 @@ static void op_pci_write(QTestState *s, const unsigned char * data, size_t len) } } +static void op_add_dma_pattern(QTestState *s, + const unsigned char *data, size_t len) +{ + struct { + /* + * index and stride can be used to increment the index-th byte of the + * pattern by the value stride, for each loop of the pattern. + */ + uint8_t index; + uint8_t stride; + } a; + + if (len < sizeof(a) + 1) { + return; + } + memcpy(&a, data, sizeof(a)); + pattern p = {a.index, a.stride, len - sizeof(a), data + sizeof(a)}; + p.index = a.index % p.len; + g_array_append_val(dma_patterns, p); + return; +} + +static void op_clear_dma_patterns(QTestState *s, + const unsigned char *data, size_t len) +{ + g_array_set_size(dma_patterns, 0); + dma_pattern_index = 0; +} + static void op_clock_step(QTestState *s, const unsigned char *data, size_t len) { qtest_clock_step_next(s); @@ -396,6 +559,8 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size) [OP_WRITE] = op_write, [OP_PCI_READ] = op_pci_read, [OP_PCI_WRITE] = op_pci_write, + [OP_ADD_DMA_PATTERN] = op_add_dma_pattern, + [OP_CLEAR_DMA_PATTERNS] = op_clear_dma_patterns, [OP_CLOCK_STEP] = op_clock_step, }; const unsigned char *cmd = Data; @@ -425,6 +590,8 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size) setitimer(ITIMER_VIRTUAL, &timer, NULL); } + op_clear_dma_patterns(s, NULL, 0); + while (cmd && Size) { /* Get the length until the next command or end of input */ nextcmd = memmem(cmd, Size, SEPARATOR, strlen(SEPARATOR)); @@ -441,6 +608,7 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size) /* Advance to the next command */ cmd = nextcmd ? nextcmd + sizeof(SEPARATOR) - 1 : nextcmd; Size = Size - (cmd_len + sizeof(SEPARATOR) - 1); + g_array_set_size(dma_regions, 0); } _Exit(0); } else { @@ -455,6 +623,9 @@ static void usage(void) printf("QEMU_FUZZ_ARGS= the command line arguments passed to qemu\n"); printf("QEMU_FUZZ_OBJECTS= " "a space separated list of QOM type names for objects to fuzz\n"); + printf("Optionally: QEMU_AVOID_DOUBLE_FETCH= " + "Try to avoid racy DMA double fetch bugs? %d by default\n", + avoid_double_fetches); printf("Optionally: QEMU_FUZZ_TIMEOUT= Specify a custom timeout (us). " "0 to disable. %d by default\n", timeout); exit(0); @@ -522,9 +693,16 @@ static void general_pre_fuzz(QTestState *s) if (!getenv("QEMU_FUZZ_OBJECTS")) { usage(); } + if (getenv("QEMU_AVOID_DOUBLE_FETCH")) { + avoid_double_fetches = 1; + } if (getenv("QEMU_FUZZ_TIMEOUT")) { timeout = g_ascii_strtoll(getenv("QEMU_FUZZ_TIMEOUT"), NULL, 0); } + qts_global = s; + + dma_regions = g_array_new(false, false, sizeof(address_range)); + dma_patterns = g_array_new(false, false, sizeof(pattern)); fuzzable_memoryregions = g_ptr_array_new(); fuzzable_pci_devices = g_ptr_array_new();
When a virtual-device tries to access some buffer in memory over DMA, we add call-backs into the fuzzer(next commit). The fuzzer checks verifies that the DMA request maps to a physical RAM address and fills the memory with fuzzer-provided data. The patterns that we use to fill this memory are specified using add_dma_pattern and clear_dma_patterns operations. Signed-off-by: Alexander Bulekov <alxndr@bu.edu> --- tests/qtest/fuzz/general_fuzz.c | 178 ++++++++++++++++++++++++++++++++ 1 file changed, 178 insertions(+)