Re: [PATCH] efi: Initialize canary to non-zero value

[Daniel Kiper]

On Sun, Nov 12, 2023 at 08:22:42AM +0100, Heinrich Schuchardt wrote:
> On 11/12/23 04:23, Glenn Washburn wrote:
> > The canary, __stack_chk_guard, is in the BSS and so will get initialized to
> > zero if it is not explicitly initialized. If the UEFI firmware does not
> > support the RNG protocol, then the canary will not be randomized and will
> > be used as zero. This seems like a possibly easier value to write by an
> > attacker. Initialize canary to static random bytes, so that it is still
> > random when there is not RNG protocol.
> >
> > Signed-off-by: Glenn Washburn <development@efficientek.com>
>
> Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

> > ---
> >   grub-core/kern/efi/init.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/grub-core/kern/efi/init.c b/grub-core/kern/efi/init.c
> > index 0e28bea17a76..b85d98ca47fd 100644
> > --- a/grub-core/kern/efi/init.c
> > +++ b/grub-core/kern/efi/init.c
> > @@ -41,7 +41,7 @@ static grub_guid_t rng_protocol_guid = 
> > GRUB_EFI_RNG_PROTOCOL_GUID;
> >
> >   static grub_efi_uint8_t stack_chk_guard_buf[32];
> >
> > -grub_addr_t __stack_chk_guard;
> > +grub_addr_t __stack_chk_guard = (grub_addr_t) 0x92f2b7e2f193b25c;

I would add last sentence from the commit message before this line.
I can do it for you before push...

> >
> >   void __attribute__ ((noreturn))
> >   __stack_chk_fail (void)

Daniel