Re: [PATCH 2/2] uimage: disable zero page when loading to SDRAM at address 0x0

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 10/14/20 5:08 PM, Michael Tretter wrote:
> If the SDRAM is mapped to address 0x0 and an image should be loaded to
> to the SDRAM without offset, Barebox would normally trap the access as a
> null pointer.
> 
> However, since Linux kernel commit cfa7ede20f13 ("arm64: set TEXT_OFFSET
> to 0x0 in preparation for removing it entirely") no offset is the
> default for arm64. Therefore, copying the image to 0x0 of the SDRAM is
> necessary.
> 
> Disable the zero page trap for copying an image to address 0x0.
> 
> Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
> ---
>  common/uimage.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/common/uimage.c b/common/uimage.c
> index a84b8fddc4e7..b1e9b402e98a 100644
> --- a/common/uimage.c
> +++ b/common/uimage.c
> @@ -27,6 +27,7 @@
>  #include <rtc.h>
>  #include <filetype.h>
>  #include <memory.h>
> +#include <zero_page.h>
>  
>  static inline int uimage_is_multi_image(struct uimage_handle *handle)
>  {
> @@ -359,7 +360,13 @@ static int uimage_sdram_flush(void *buf, unsigned int len)
>  		}
>  	}
>  
> -	memcpy(uimage_buf + uimage_size, buf, len);
> +	if (zero_page_contains((unsigned long)uimage_buf + uimage_size)) {
> +		zero_page_disable();
> +		memcpy(uimage_buf + uimage_size, buf, len);
> +		zero_page_enable();

If this remains, please add a memcpy_notrap or something.

> +	} else {
> +		memcpy(uimage_buf + uimage_size, buf, len);
> +	}
>  
>  	uimage_size += len;
>  
> @@ -388,7 +395,14 @@ struct resource *file_to_sdram(const char *filename, unsigned long adr)
>  			goto out;
>  		}
>  
> -		now = read_full(fd, (void *)(res->start + ofs), BUFSIZ);
> +		if (zero_page_contains(res->start + ofs)) {
> +			zero_page_disable();
> +			now = read_full(fd, (void *)(res->start + ofs), BUFSIZ);
> +			zero_page_enable();

And use that new memcpy_notrap here to copy from an intermediate buffer. You open quite a can
of worms when you treat NULL as a valid address. Better have this contained in a single
file instead of hoping the compiler doesn't do a NULL-can't-happen-here optimization
in all that block/cdev/fs code that read_full may call into.

> +		} else {
> +			now = read_full(fd, (void *)(res->start + ofs), BUFSIZ);
> +		}
> +
>  		if (now < 0) {
>  			release_sdram_region(res);
>  			res = NULL;
> 

-- 
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