Re: [PATCH] x86/efistub: fix the missing KASLR_FLAG bit in boot_params->hdr.loadflags

[Tom Lendacky]

On 1/2/24 09:29, Ard Biesheuvel wrote:
> On Tue, 26 Dec 2023 at 15:03, Yuntao Wang <ytcoode@xxxxxxxxx> wrote:
> > When KASLR is enabled, the KASLR_FLAG bit in boot_params->hdr.loadflags
> > should be set to 1 to propagate KASLR status from compressed kernel to
> > kernel, just as the choose_random_location() function does.
> >
> > Currently, when kernel is booted via efi stub, the KASLR_FLAG bit in
> > boot_params->hdr.loadflags is not set, even though it should be. This
> > causes some functions, such as kernel_randomize_memory(), not to execute
> > as expected. Fix it.
> >
> > Signed-off-by: Yuntao Wang <ytcoode@xxxxxxxxx>
> > ---
> >   drivers/firmware/efi/libstub/x86-stub.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> > index da9b7b8d0716..b0c68593ad40 100644
> > --- a/drivers/firmware/efi/libstub/x86-stub.c
> > +++ b/drivers/firmware/efi/libstub/x86-stub.c
> > @@ -787,7 +787,10 @@ static efi_status_t efi_decompress_kernel(unsigned long *kernel_entry)
> >                          efi_debug("AMI firmware v2.0 or older detected - disabling physical KASLR\n");
> >                          seed[0] = 0;
> >                  }
> > -       }
> > +
> > +               boot_params_ptr->hdr.loadflags |= KASLR_FLAG;
> > +       } else
> > +               boot_params_ptr->hdr.loadflags &= ~KASLR_FLAG;
>
> Thanks for the fix.

Does it need a Fixes: tag?

Thanks,
Tom

> I'll queue this up right away, but I am going to drop the 'else' part,
> given that the KASLR flag is never set by the EFI stub so clearing it
> should never be needed.
>
>
> >          status = efi_random_alloc(alloc_size, CONFIG_PHYSICAL_ALIGN, &addr,
> >                                    seed[0], EFI_LOADER_CODE,
> > --
> > 2.43.0