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Date: Fri, 31 Jul 2015 23:01:48 +0800
From: joeyli <jlee@...e.com>
To: Matt Fleming <matt.fleming@...el.com>
Cc: "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
Matthew Garrett <matthew.garrett@...ula.com>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
Josh Boyer <jwboyer@...hat.com>,
Vojtech Pavlik <vojtech@...e.cz>,
Jiri Kosina <jkosina@...e.cz>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 05/16] x86/efi: Get entropy through EFI random number
generator protocol
On Fri, Jul 31, 2015 at 10:59:12PM +0800, joeyli wrote:
> On Thu, Jul 30, 2015 at 05:11:44PM +0100, Matt Fleming wrote:
> > On Thu, 2015-07-16 at 22:25 +0800, Lee, Chun-Yi wrote:
> > > To grab random numbers through EFI protocol as one of the entropies
> > > source of swsusp key, this patch adds the logic for accessing EFI RNG
> > > (random number generator) protocol that's introduced since UEFI 2.4.
> > >
> > > Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
> > > ---
> > > arch/x86/boot/compressed/efi_random.c | 193 ++++++++++++++++++++++++++++++++++
> > > include/linux/efi.h | 46 ++++++++
> > > 2 files changed, 239 insertions(+)
> >
> > [...]
> >
> > > @@ -2,6 +2,191 @@
> > >
> > > #include <linux/efi.h>
> > > #include <asm/archrandom.h>
> > > +#include <asm/efi.h>
> > > +
> > > +static efi_status_t efi_locate_rng(efi_system_table_t *sys_table,
> > > + void ***rng_handle)
> > > +{
> > > + efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
> > > + unsigned long size = 0;
> > > + efi_status_t status;
> > > +
> > > + status = efi_call_early(locate_handle,
> > > + EFI_LOCATE_BY_PROTOCOL,
> > > + &rng_proto, NULL, &size, *rng_handle);
> > > +
> > > + if (status == EFI_BUFFER_TOO_SMALL) {
> > > + status = efi_call_early(allocate_pool,
> > > + EFI_LOADER_DATA,
> > > + size, (void **)rng_handle);
> > > +
> > > + if (status != EFI_SUCCESS) {
> > > + efi_printk(sys_table, " Failed to alloc mem for rng_handle");
> > > + return status;
> > > + }
> > > +
> > > + status = efi_call_early(locate_handle,
> > > + EFI_LOCATE_BY_PROTOCOL, &rng_proto,
> > > + NULL, &size, *rng_handle);
> > > + }
> > > +
> > > + if (status != EFI_SUCCESS) {
> > > + efi_printk(sys_table, " Failed to locate EFI_RNG_PROTOCOL");
> > > + goto free_handle;
> > > + }
> > > +
> > > + return EFI_SUCCESS;
> > > +
> > > +free_handle:
> > > + efi_call_early(free_pool, *rng_handle);
> > > +
> > > + return status;
> > > +}
> >
> > I would suggest setting *rng_handle = NULL at the beginning of this
> > function just because if we ever forget to set it that way in the caller
> > this free_pool call might do screwy things.
> >
>
> Thanks for your suggestion, I will set NULL to *rng_handle.
>
> >
> > > +static bool efi_rng_supported(efi_system_table_t *sys_table)
> > > +{
> > > + const struct efi_config *efi_early = __efi_early();
> > > + u32 random = 0;
> > > + efi_status_t status;
> > > + void **rng_handle = NULL;
> > > +
> > > + status = efi_locate_rng(sys_table, &rng_handle);
> > > + if (status != EFI_SUCCESS)
> > > + return false;
> > > +
> > > + if (efi_early->is64)
> > > + random = efi_rng_supported64(sys_table, rng_handle);
> > > + else
> > > + random = efi_rng_supported32(sys_table, rng_handle);
> > > +
> > > + efi_call_early(free_pool, rng_handle);
> > > +
> > > + return random;
> >
> > Oops, 'random' isn't a bool but it should be.
> >
>
> I will change type of random to boot.
>
> > > @@ -51,6 +236,14 @@ static unsigned long get_random_long(unsigned long entropy,
> > > use_i8254 = false;
> > > }
> > >
> > > + if (efi_rng_supported(sys_table)) {
> > > + efi_printk(sys_table, " EFI_RNG");
> > > + raw = efi_get_rng(sys_table);
> > > + if (raw)
> > > + random ^= raw;
> > > + use_i8254 = false;
> > > + }
> > > +
> > > if (use_i8254) {
> > > efi_printk(sys_table, " i8254");
> > > random ^= i8254();
> >
> > Have you looked at the tradeoff in terms of boot time for building a key
> > array in 'unsigned long' chunks as opposed to passing the array and size
> > directly for the RNG protocol?
> >
>
> I didn't really measure the speed, but directly passing array and size to
> RNG protocol should a bit faster than calling the protocol a could of times.
>
> But, the key generation process only in first time building or trigger by
> user raises the rebuild flag. So, it doesn't affect to every booting time.
>
> Due to I want let the whole key array more random, so each unsigned long
> chunk was mixed(xor) by following entropy:
> + random long from RDRAND
> + RDTSC
> + random long from EFI RNG protocol
> + last unsigned long chunk
>
> Another reason is voiding the result of EFI RNG protocol to get weight
^^^^^^^^^ avoiding
Sorry for my typo!
> higher than other source, in case too trust EFI RNG.
Joey Lee
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