Re: [PATCH v2 03/15] fuzz: Add PCI features to the general fuzzer

[Darren Kenny]

On Wednesday, 2020-08-19 at 02:10:58 -04, Alexander Bulekov wrote:
> This patch compares TYPE_PCI_DEVICE objects against the user-provided
> matching pattern. If there is a match, we use some hacks and leverage
> QOS to map each possible BAR for that device. Now fuzzed inputs might be
> converted to pci_read/write commands which target specific. This means
> that we can fuzz a particular device's PCI configuration space,
>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

Thanks,

Darren.

> ---
>  tests/qtest/fuzz/general_fuzz.c | 83 +++++++++++++++++++++++++++++++++
>  1 file changed, 83 insertions(+)
>
> diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c
> index 01bcb029b1..17b572a439 100644
> --- a/tests/qtest/fuzz/general_fuzz.c
> +++ b/tests/qtest/fuzz/general_fuzz.c
> @@ -24,6 +24,7 @@
>  #include "exec/ramblock.h"
>  #include "exec/address-spaces.h"
>  #include "hw/qdev-core.h"
> +#include "hw/pci/pci.h"
>  
>  /*
>   * SEPARATOR is used to separate "operations" in the fuzz input
> @@ -35,12 +36,17 @@ enum cmds{
>      OP_OUT,
>      OP_READ,
>      OP_WRITE,
> +    OP_PCI_READ,
> +    OP_PCI_WRITE,
>      OP_CLOCK_STEP,
>  };
>  
>  #define DEFAULT_TIMEOUT_US 100000
>  #define USEC_IN_SEC 100000000
>  
> +#define PCI_HOST_BRIDGE_CFG 0xcf8
> +#define PCI_HOST_BRIDGE_DATA 0xcfc
> +
>  typedef struct {
>      size_t addr;
>      size_t len; /* The number of bytes until the end of the I/O region */
> @@ -52,6 +58,8 @@ static useconds_t timeout = 100000;
>   * user for fuzzing.
>   */
>  static GPtrArray *fuzzable_memoryregions;
> +static GPtrArray *fuzzable_pci_devices;
> +
>  /*
>   * 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
> @@ -283,6 +291,65 @@ static void op_write(QTestState *s, const unsigned char 
> * data, size_t len)
>          break;
>      }
>  }
> +static void op_pci_read(QTestState *s, const unsigned char * data, size_t 
> len)
> +{
> +    enum Sizes {Byte, Word, Long, end_sizes};
> +    struct {
> +        uint8_t size;
> +        uint8_t base;
> +        uint8_t offset;
> +    } a;
> +    if (len < sizeof(a) || fuzzable_pci_devices->len == 0) {
> +        return;
> +    }
> +    memcpy(&a, data, sizeof(a));
> +    PCIDevice *dev = g_ptr_array_index(fuzzable_pci_devices,
> +                                  a.base % fuzzable_pci_devices->len);
> +    int devfn = dev->devfn;
> +    qtest_outl(s, PCI_HOST_BRIDGE_CFG, (1U << 31) | (devfn << 8) | a.offset);
> +    switch (a.size %= end_sizes) {
> +    case Byte:
> +        qtest_inb(s, PCI_HOST_BRIDGE_DATA);
> +        break;
> +    case Word:
> +        qtest_inw(s, PCI_HOST_BRIDGE_DATA);
> +        break;
> +    case Long:
> +        qtest_inl(s, PCI_HOST_BRIDGE_DATA);
> +        break;
> +    }
> +}
> +
> +static void op_pci_write(QTestState *s, const unsigned char * data, size_t 
> len)
> +{
> +    enum Sizes {Byte, Word, Long, end_sizes};
> +    struct {
> +        uint8_t size;
> +        uint8_t base;
> +        uint8_t offset;
> +        uint32_t value;
> +    } a;
> +    if (len < sizeof(a) || fuzzable_pci_devices->len == 0) {
> +        return;
> +    }
> +    memcpy(&a, data, sizeof(a));
> +    PCIDevice *dev = g_ptr_array_index(fuzzable_pci_devices,
> +                                  a.base % fuzzable_pci_devices->len);
> +    int devfn = dev->devfn;
> +    qtest_outl(s, PCI_HOST_BRIDGE_CFG, (1U << 31) | (devfn << 8) | a.offset);
> +    switch (a.size %= end_sizes) {
> +    case Byte:
> +        qtest_outb(s, PCI_HOST_BRIDGE_DATA, a.value & 0xFF);
> +        break;
> +    case Word:
> +        qtest_outw(s, PCI_HOST_BRIDGE_DATA, a.value & 0xFFFF);
> +        break;
> +    case Long:
> +        qtest_outl(s, PCI_HOST_BRIDGE_DATA, a.value & 0xFFFFFFFF);
> +        break;
> +    }
> +}
> +
>  static void op_clock_step(QTestState *s, const unsigned char *data, size_t 
> len)
>  {
>      qtest_clock_step_next(s);
> @@ -327,6 +394,8 @@ static void general_fuzz(QTestState *s, const unsigned 
> char *Data, size_t Size)
>          [OP_OUT]                = op_out,
>          [OP_READ]               = op_read,
>          [OP_WRITE]              = op_write,
> +        [OP_PCI_READ]           = op_pci_read,
> +        [OP_PCI_WRITE]          = op_pci_write,
>          [OP_CLOCK_STEP]         = op_clock_step,
>      };
>      const unsigned char *cmd = Data;
> @@ -418,6 +487,19 @@ static int locate_fuzz_objects(Object *child, void 
> *opaque)
>      if (g_pattern_match_simple(pattern, object_get_typename(child))) {
>          /* Find and save ptrs to any child MemoryRegions */
>          object_child_foreach_recursive(child, locate_fuzz_memory_regions, 
> NULL);
> +
> +        /*
> +         * We matched an object. If its a PCI device, store a pointer to it 
> so
> +         * we can map BARs and fuzz its config space.
> +         */
> +        if (object_dynamic_cast(OBJECT(child), TYPE_PCI_DEVICE)) {
> +            /*
> +             * Don't want duplicate pointers to the same PCIDevice, so remove
> +             * copies of the pointer, before adding it.
> +             */
> +            g_ptr_array_remove_fast(fuzzable_pci_devices, PCI_DEVICE(child));
> +            g_ptr_array_add(fuzzable_pci_devices, PCI_DEVICE(child));
> +        }
>      } else if (object_dynamic_cast(OBJECT(child), TYPE_MEMORY_REGION)) {
>          if (g_pattern_match_simple(pattern,
>              object_get_canonical_path_component(child))) {
> @@ -445,6 +527,7 @@ static void general_pre_fuzz(QTestState *s)
>      }
>  
>      fuzzable_memoryregions = g_ptr_array_new();
> +    fuzzable_pci_devices   = g_ptr_array_new();
>      char **result = g_strsplit (getenv("QEMU_FUZZ_OBJECTS"), " ", -1);
>      for (int i = 0; result[i] != NULL; i++) {
>          printf("Matching objects by name %s\n", result[i]);
> -- 
> 2.27.0