Subject: Re: [RFC PATCH] ARM: zynq: Use memcpy_toio instead of memcpy on smp bring-up

From: Russell King - ARM Linux admin <[email-masked]>
Date: Tue, 30 Jul 2019 11:47:46 +0100

On Tue, Jul 30, 2019 at 12:43:26AM -0400, Luis Araneda wrote:
> This fixes a kernel panic (read overflow) on memcpy when
> FORTIFY_SOURCE is enabled.
> 
> The computed size of memcpy args are:
> - p_size (dst): 4294967295 = (size_t) -1
> - q_size (src): 1
> - size (len): 8
> 
> Additionally, the memory is marked as __iomem, so one of
> the memcpy_* functions should be used for read/write
> 
> Signed-off-by: Luis Araneda <[email-masked]>
> ---
> 
> For anyone trying to reproduce / debug this, it panics
> before the console has any output.
> I used JTAG to find the panic, but I had to comment-out
> the call to "zynq_slcr_cpu_stop" as it stops the JTAG
> interface and the connection is dropped, at least with OpenOCD.
> 
> I run-tested this on a Digilent Zybo Z7 board
> ---
>  arch/arm/mach-zynq/platsmp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-zynq/platsmp.c b/arch/arm/mach-zynq/platsmp.c
> index a7cfe07156f4..407abade7336 100644
> --- a/arch/arm/mach-zynq/platsmp.c
> +++ b/arch/arm/mach-zynq/platsmp.c
> @@ -57,7 +57,7 @@ int zynq_cpun_start(u32 address, int cpu)
>  			* 0x4: Jump by mov instruction
>  			* 0x8: Jumping address
>  			*/
> -			memcpy((__force void *)zero, &zynq_secondary_trampoline,
> +			memcpy_toio(zero, &zynq_secondary_trampoline,
>  							trampoline_size);
>  			writel(address, zero + trampoline_size);

I'm not convinced that this is correct.  It looks like
zynq_secondary_trampoline could be either ARM or Thumb code - there is
no .arm directive before it.  If it's ARM code, then this is fine.  If
Thumb code, then zynq_secondary_trampoline will be offset by one, and
we will miss copying the first byte of code.

-- 
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