Re: [PATCH v2 13/16] arm: uncompress: verify sha256 if enabled

[Lucas Stach <l.stach@pengutronix.de>]

Am Montag, den 05.08.2019, 11:23 +0200 schrieb Rouven Czerwinski:
> Add piggydata verification before the ARM uncompress function.
> This calculates the sha256sum of the compressed barebox binary and only
> continues if the builtin sha256sum matches the calculated sha256sum.
> 
> > Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
> ---
>  arch/arm/cpu/uncompress.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/cpu/uncompress.c b/arch/arm/cpu/uncompress.c
> index c7851c5..4c69b4c 100644
> --- a/arch/arm/cpu/uncompress.c
> +++ b/arch/arm/cpu/uncompress.c
> @@ -42,14 +42,18 @@ unsigned long free_mem_end_ptr;
>  extern unsigned char input_data[];
>  extern unsigned char input_data_end[];
>  
> +extern unsigned char sha_sum[];
> +extern unsigned char sha_sum_end[];
> +
>  void __noreturn barebox_multi_pbl_start(unsigned long membase,
> >  		unsigned long memsize, void *boarddata)
>  {
> > -	uint32_t pg_len, uncompressed_len;
> > +	uint32_t pg_len, uncompressed_len, pbl_hash_len;
> >  	void __noreturn (*barebox)(unsigned long, unsigned long, void *);
> >  	unsigned long endmem = membase + memsize;
> >  	unsigned long barebox_base;
> >  	void *pg_start, *pg_end;
> > +	void *pbl_hash_start, *pbl_hash_end;
> >  	unsigned long pc = get_pc();
>  
> >  	pg_start = input_data + global_variable_offset();
> @@ -92,6 +96,17 @@ void __noreturn barebox_multi_pbl_start(unsigned long membase,
> >  	pr_debug("uncompressing barebox binary at 0x%p (size 0x%08x) to 0x%08lx (uncompressed size: 0x%08x)\n",
> >  			pg_start, pg_len, barebox_base, uncompressed_len);
>  
> > +	if (IS_ENABLED(CONFIG_PBL_VERIFY_PIGGY)) {
> > +		pbl_hash_start = sha_sum + global_variable_offset();
> +		pbl_hash_end = sha_sum_end + global_variable_offset();

This code is executed after relocation, so there is no point in adding
the global variable offset. It doesn't harm, as the offset is always 0
at that point, but better don't start cargo-culting here.

Regards,
Lucas

> +		pbl_hash_len = pbl_hash_end - pbl_hash_start;
> > +		if (pbl_barebox_verify(pg_start, pg_len, pbl_hash_start,
> > +				       pbl_hash_len) != 0) {
> > +			putc_ll('!');
> > +			panic("hash mismatch, refusing to decompress");
> > +		}
> > +	}
> +
> >  	pbl_barebox_uncompress((void*)barebox_base, pg_start, pg_len);
>  
> >  	sync_caches_for_execution();

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