lkml.org 
[lkml]   [2015]   [May]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 3/3] vTPM: support little endian guests
Thank you Vicky and Joy for the clarification.  This patch mainly 
converts the fields in the tcpa_event structure. I see the code converts
everytime it accesses the event fields. Would it be more efficient if you
do the conversion once and reuse them when needed? Could
convert_to_host_format(x) takes x as a tcpa_event structure?
If not you still can convert individual fields and reuse them. I'm aware
that the pcr_value field is type u8 and it does not need the conversion
but if convert_to_host_format() can convert the structure it shouldn't convert
u8 type I think.

> static const char* tcpa_event_type_strings[] = {
> "PREBOOT",
> @@ -82,9 +87,11 @@ static void *tpm_bios_measurements_start(struct seq_file *m, loff_t *pos)
> event = addr;
>
> if ((addr + sizeof(struct tcpa_event)) < limit) {
> - if (event->event_type == 0 && event->event_size == 0)
> + if ((convert_to_host_format(event->event_type) == 0) &&
> + (convert_to_host_format(event->event_size) == 0))
> return NULL;
> - addr += sizeof(struct tcpa_event) + event->event_size;
> + addr += (sizeof(struct tcpa_event) +
> + convert_to_host_format(event->event_size));
> }
> }
>
> @@ -94,8 +101,11 @@ static void *tpm_bios_measurements_start(struct seq_file *m, loff_t *pos)
>
> event = addr;
>
> - if ((event->event_type == 0 && event->event_size == 0) ||
> - ((addr + sizeof(struct tcpa_event) + event->event_size) >= limit))
> + if (((convert_to_host_format(event->event_type) == 0) &&
> + (convert_to_host_format(event->event_size) == 0))
> + ||
> + ((addr + sizeof(struct tcpa_event) +
> + convert_to_host_format(event->event_size)) >= limit))
> return NULL;
>
> return addr;

In this function, event_type and event_size can be converted
once and reuse.

> case SEPARATOR:
> case ACTION:
> - if (MAX_TEXT_EVENT > event->event_size) {
> + if (MAX_TEXT_EVENT >
> + convert_to_host_format(event->event_size)) {
> name = event_entry;
> - n_len = event->event_size;
> + n_len = convert_to_host_format(event->event_size);
> }
> break;
> case EVENT_TAG:

Same here.

> @@ -208,11 +229,43 @@ static int tpm_binary_bios_measurements_show(struct seq_file *m, void *v)
> struct tcpa_event *event = v;
> char *data = v;
> int i;
> -
> - for (i = 0; i < sizeof(struct tcpa_event) + event->event_size; i++)
> + u32 x;
> + char tmp[4];
> +
> + /* PCR */
> + x = convert_to_host_format(event->pcr_index);
> + memcpy(tmp, &x, 4);
> + for (i = 0; i < 4; i++)
> + seq_putc(m, tmp[i]);
> + data += 4;
> +
> + /* Event Type */
> + x = convert_to_host_format(event->event_type);
> + memcpy(tmp, &x, 4);
> + for (i = 0; i < 4; i++)
> + seq_putc(m, tmp[i]);
> + data += 4;
> +
> + /* HASH */
> + for (i = 0; i < 20; i++)
> seq_putc(m, data[i]);
> + data += 20;
> +
> + /* Size */
> + x = convert_to_host_format(event->event_size);
> + memcpy(tmp, &x, 4);
> + for (i = 0; i < 4; i++)
> + seq_putc(m, tmp[i]);
> + data += 4;
> +
> + /* Data */
> + if (convert_to_host_format(event->event_size)) {
> + for (i = 0; i < convert_to_host_format(event->event_size); i++)
> + seq_putc(m, data[i]);
> + }
>
> return 0;
> +
> }
If the tcpa_event structure is converted, you may be able to get away
with memcpy and the for loop.

Thanks,
--Ashley Lai


\
 
 \ /
  Last update: 2015-05-19 23:21    [W:0.099 / U:1.212 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site