linux-kernel - Re: [PATCH] tpm: of: avoid __va() translation for event log address

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Date:   Fri, 25 Sep 2020 08:56:26 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH] tpm: of: avoid __va() translation for event log address

On Tue, Sep 22, 2020 at 11:41:28AM +0200, Ard Biesheuvel wrote:
> The TPM event log is provided to the OS by the firmware, by loading
> it into an area in memory and passing the physical address via a node
> in the device tree.
> 
> Currently, we use __va() to access the memory via the kernel's linear
> map: however, it is not guaranteed that the linear map covers this
> particular address, as we may be running under HIGHMEM on a 32-bit
> architecture, or running firmware that uses a memory type for the
> event log that is omitted from the linear map (such as EfiReserved).

Makes perfect sense to the level that I wonder if this should have a
fixes tag and/or needs to be backported to the stable kernels?

> So instead, use memremap(), which will reuse the linear mapping if
> it is valid, or create another mapping otherwise.
> 
> Cc: Peter Huewe <peterhuewe@....de>
> Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  drivers/char/tpm/eventlog/of.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/eventlog/of.c b/drivers/char/tpm/eventlog/of.c
> index a9ce66d09a75..9178547589a3 100644
> --- a/drivers/char/tpm/eventlog/of.c
> +++ b/drivers/char/tpm/eventlog/of.c
> @@ -11,6 +11,7 @@
>   */
>  
>  #include <linux/slab.h>
> +#include <linux/io.h>
>  #include <linux/of.h>
>  #include <linux/tpm_eventlog.h>
>  
> @@ -25,6 +26,7 @@ int tpm_read_log_of(struct tpm_chip *chip)
>  	struct tpm_bios_log *log;
>  	u32 size;
>  	u64 base;
> +	void *p;

I'd just use 'ptr' for readability sake.

>  	log = &chip->log;
>  	if (chip->dev.parent && chip->dev.parent->of_node)
> @@ -65,7 +67,11 @@ int tpm_read_log_of(struct tpm_chip *chip)
>  		return -EIO;
>  	}
>  
> -	log->bios_event_log = kmemdup(__va(base), size, GFP_KERNEL);
> +	p = memremap(base, size, MEMREMAP_WB);
> +	if (!p)
> +		return -ENOMEM;
> +	log->bios_event_log = kmemdup(p, size, GFP_KERNEL);
> +	memunmap(p);
>  	if (!log->bios_event_log)
>  		return -ENOMEM;
>  
> -- 
> 2.17.1
> 

This is a really great catch!

I'm a bit late of my PR a bit because of SGX upstreaming madness
(sending v39 soon). If you can answer to my question above, I can do
that nitpick change to patch and get it to my v5.10 PR.

PS. Just so that you know, once I've applied it, it will be available
here:

git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git

I'll include MAINTAINERS update to that PR.

/Jarkko