Re: [RFC PATCH v2 4/5] softmmu/physmem: Introduce flatview_access_allowed() to check bus perms

[Stefan Hajnoczi]

On Mon, Aug 23, 2021 at 06:41:56PM +0200, Philippe Mathieu-Daudé wrote:
> Introduce flatview_access_allowed() to check bus permission
> before running any bus transaction. For now this is a simple
> stub.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  softmmu/physmem.c | 37 +++++++++++++++++++++++++++++++++++--
>  1 file changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index e534dc69918..0d31a2f4199 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -2754,6 +2754,27 @@ static bool prepare_mmio_access(MemoryRegion *mr)
>      return release_lock;
>  }
>  
> +/**
> + * flatview_access_allowed
> + * @mr: #MemoryRegion to be accessed
> + * @attrs: memory transaction attributes
> + * @addr: address within that memory region
> + * @len: the number of bytes to access
> + * @result: optional pointer to a MemTxResult or NULL
> + *
> + * Check if a memory transaction is allowed. If an error occurs this
> + * method will return false to indicate denial, as well as setting
> + * @result to contain corresponding #MemTxResult.
> + *
> + * Returns: true if transaction is allowed, false if denied.
> + */
> +static inline bool flatview_access_allowed(MemoryRegion *mr, MemTxAttrs 
> attrs,
> +                                           hwaddr addr, hwaddr len,
> +                                           MemTxResult *result)
> +{
> +    return true;
> +}

The callers below don't benefit from the result pointer argument. The
code would be clearer if they did:

  if (!flatview_access_allowed(...)) {
      return MEMTX_BUS_ERROR;
  }

> +
>  /* Called within RCU critical section.  */
>  static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
>                                             MemTxAttrs attrs,
> @@ -2768,7 +2789,9 @@ static MemTxResult flatview_write_continue(FlatView 
> *fv, hwaddr addr,
>      const uint8_t *buf = ptr;
>  
>      for (;;) {
> -        if (!memory_access_is_direct(mr, true)) {
> +        if (!flatview_access_allowed(mr, attrs, addr1, l, &result)) {
> +            /* 'result' contains the error, keep going. */
> +        } else if (!memory_access_is_direct(mr, true)) {
>              release_lock |= prepare_mmio_access(mr);
>              l = memory_access_size(mr, l, addr1);
>              /* XXX: could force current_cpu to NULL to avoid
> @@ -2810,9 +2833,13 @@ static MemTxResult flatview_write(FlatView *fv, hwaddr 
> addr, MemTxAttrs attrs,
>      hwaddr l;
>      hwaddr addr1;
>      MemoryRegion *mr;
> +    MemTxResult result = MEMTX_OK;
>  
>      l = len;
>      mr = flatview_translate(fv, addr, &addr1, &l, true, attrs);
> +    if (!flatview_access_allowed(mr, attrs, addr, len, &result)) {
> +        return result;
> +    }
>      return flatview_write_continue(fv, addr, attrs, buf, len,
>                                     addr1, l, mr);
>  }
> @@ -2831,7 +2858,9 @@ MemTxResult flatview_read_continue(FlatView *fv, hwaddr 
> addr,
>  
>      fuzz_dma_read_cb(addr, len, mr);
>      for (;;) {
> -        if (!memory_access_is_direct(mr, false)) {
> +        if (!flatview_access_allowed(mr, attrs, addr1, l, &result)) {
> +            /* 'result' contains the error, keep going. */
> +        } else if (!memory_access_is_direct(mr, false)) {
>              /* I/O case */
>              release_lock |= prepare_mmio_access(mr);
>              l = memory_access_size(mr, l, addr1);
> @@ -2871,9 +2900,13 @@ static MemTxResult flatview_read(FlatView *fv, hwaddr 
> addr,
>      hwaddr l;
>      hwaddr addr1;
>      MemoryRegion *mr;
> +    MemTxResult result = MEMTX_OK;
>  
>      l = len;
>      mr = flatview_translate(fv, addr, &addr1, &l, false, attrs);
> +    if (!flatview_access_allowed(mr, attrs, addr, len, &result)) {
> +        return result;
> +    }
>      return flatview_read_continue(fv, addr, attrs, buf, len,
>                                    addr1, l, mr);
>  }
> -- 
> 2.31.1
>

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