linux-kernel - Re: ACPI / LPIT: Correct LPIT end address for lpit

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Date:   Mon, 06 May 2019 16:46:15 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Lenny Szubowicz <lszubowi@...hat.com>, rjw@...ysocki.net,
        lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: ACPI / LPIT: Correct LPIT end address for lpit_process()

On Thu, 2019-05-02 at 16:00 -0400, Lenny Szubowicz wrote:
> Correct the LPIT end address which is passed into lpit_process()
> and the end address limit test in lpit_process().
> 
> The LPI state descriptor subtables follow the fixed sized
> acpi_lpit_header up to the end of the LPIT. The last LPI state
> descriptor can end at exactly the end of the LPIT.
> 
> Note that this is a fix to a latent problem. Although incorrect,
> the unpatched version works because the passed in end address
> is just slightly beyond the actual end of the LPIT and the size
> of the ACPI LPIT header is smaller than the size of the only
> currently defined LPI state descriptor, acpi_lpit_native.
> 
> Signed-off-by: Lenny Szubowicz <lszubowi@...hat.com>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>

> ---
>  drivers/acpi/acpi_lpit.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_lpit.c b/drivers/acpi/acpi_lpit.c
> index e43cb71b6972..8b170a07908a 100644
> --- a/drivers/acpi/acpi_lpit.c
> +++ b/drivers/acpi/acpi_lpit.c
> @@ -137,7 +137,7 @@ static void lpit_update_residency(struct
> lpit_residency_info *info,
>  
>  static void lpit_process(u64 begin, u64 end)
>  {
> -	while (begin + sizeof(struct acpi_lpit_native) < end) {
> +	while (begin + sizeof(struct acpi_lpit_native) <= end) {
>  		struct acpi_lpit_native *lpit_native = (struct
> acpi_lpit_native *)begin;
>  
>  		if (!lpit_native->header.type && !lpit_native-
> >header.flags) {
> @@ -156,7 +156,6 @@ static void lpit_process(u64 begin, u64 end)
>  void acpi_init_lpit(void)
>  {
>  	acpi_status status;
> -	u64 lpit_begin;
>  	struct acpi_table_lpit *lpit;
>  
>  	status = acpi_get_table(ACPI_SIG_LPIT, 0, (struct
> acpi_table_header **)&lpit);
> @@ -164,6 +163,6 @@ void acpi_init_lpit(void)
>  	if (ACPI_FAILURE(status))
>  		return;
>  
> -	lpit_begin = (u64)lpit + sizeof(*lpit);
> -	lpit_process(lpit_begin, lpit_begin + lpit->header.length);
> +	lpit_process((u64)lpit + sizeof(*lpit),
> +		     (u64)lpit + lpit->header.length);
>  }