Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1694703 > unrolled thread
| Started by | Matt Fleming <matt@codeblueprint.co.uk> |
|---|---|
| First post | 2017-07-24 15:20 +0200 |
| Last post | 2017-07-25 08:30 +0200 |
| Articles | 2 — 2 participants |
Back to article view | Back to linux.kernel
This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by
below is the oldest one visible, not the original post.
Re: [PATCH v3 1/2] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice Matt Fleming <matt@codeblueprint.co.uk> - 2017-07-24 15:20 +0200
Re: [PATCH v3 1/2] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-07-25 08:30 +0200
| From | Matt Fleming <matt@codeblueprint.co.uk> |
|---|---|
| Date | 2017-07-24 15:20 +0200 |
| Subject | Re: [PATCH v3 1/2] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice |
| Message-ID | <u6Lrc-5li-13@gated-at.bofh.it> |
On Mon, 10 Jul, at 02:51:35PM, Naoya Horiguchi wrote:
> KASLR chooses kernel location from E820_TYPE_RAM regions by walking over
> e820 entries now. E820_TYPE_RAM includes EFI_BOOT_SERVICES_CODE and
> EFI_BOOT_SERVICES_DATA, so those regions can be the target. According to
> UEFI spec, all memory regions marked as EfiBootServicesCode and
> EfiBootServicesData are available for free memory after the first call
> of ExitBootServices(). So such regions should be usable for kernel on
> spec basis.
>
> In x86, however, we have some workaround for broken firmware, where we
> keep such regions reserved until SetVirtualAddressMap() is done.
> See the following code in should_map_region():
>
> static bool should_map_region(efi_memory_desc_t *md)
> {
> ...
> /*
> * Map boot services regions as a workaround for buggy
> * firmware that accesses them even when they shouldn't.
> *
> * See efi_{reserve,free}_boot_services().
> */
> if (md->type == EFI_BOOT_SERVICES_CODE ||
> md->type == EFI_BOOT_SERVICES_DATA)
> return false;
>
> This workaround suppressed a boot crash, but potential issues still
> remain because no one prevents the regions from overlapping with kernel
> image by KASLR.
>
> So let's make sure that EFI_BOOT_SERVICES_{CODE|DATA} regions are never
> chosen as kernel memory for the workaround to work fine.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
> v2 -> v3:
> - skip EFI_LOADER_CODE and EFI_LOADER_DATA in region scan
>
> v1 -> v2:
> - switch efi_mirror_found to local variable
> - insert break when EFI_MEMORY_MORE_RELIABLE found
> ---
> arch/x86/boot/compressed/kaslr.c | 44 +++++++++++++++++++++++++++++-----------
> 1 file changed, 32 insertions(+), 12 deletions(-)
I think the patch content is fine, but please update the comments and
the changelog to say why EFI_CONVENTIONAL_MEMORY was chosen, i.e. that
it's the only memory type that we know to be free.
[toc] | [next] | [standalone]
| From | Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> |
|---|---|
| Date | 2017-07-25 08:30 +0200 |
| Message-ID | <u71vX-7IB-3@gated-at.bofh.it> |
| In reply to | #1694703 |
On Mon, Jul 24, 2017 at 02:17:07PM +0100, Matt Fleming wrote:
> On Mon, 10 Jul, at 02:51:35PM, Naoya Horiguchi wrote:
> > KASLR chooses kernel location from E820_TYPE_RAM regions by walking over
> > e820 entries now. E820_TYPE_RAM includes EFI_BOOT_SERVICES_CODE and
> > EFI_BOOT_SERVICES_DATA, so those regions can be the target. According to
> > UEFI spec, all memory regions marked as EfiBootServicesCode and
> > EfiBootServicesData are available for free memory after the first call
> > of ExitBootServices(). So such regions should be usable for kernel on
> > spec basis.
> >
> > In x86, however, we have some workaround for broken firmware, where we
> > keep such regions reserved until SetVirtualAddressMap() is done.
> > See the following code in should_map_region():
> >
> > static bool should_map_region(efi_memory_desc_t *md)
> > {
> > ...
> > /*
> > * Map boot services regions as a workaround for buggy
> > * firmware that accesses them even when they shouldn't.
> > *
> > * See efi_{reserve,free}_boot_services().
> > */
> > if (md->type == EFI_BOOT_SERVICES_CODE ||
> > md->type == EFI_BOOT_SERVICES_DATA)
> > return false;
> >
> > This workaround suppressed a boot crash, but potential issues still
> > remain because no one prevents the regions from overlapping with kernel
> > image by KASLR.
> >
> > So let's make sure that EFI_BOOT_SERVICES_{CODE|DATA} regions are never
> > chosen as kernel memory for the workaround to work fine.
> >
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > ---
> > v2 -> v3:
> > - skip EFI_LOADER_CODE and EFI_LOADER_DATA in region scan
> >
> > v1 -> v2:
> > - switch efi_mirror_found to local variable
> > - insert break when EFI_MEMORY_MORE_RELIABLE found
> > ---
> > arch/x86/boot/compressed/kaslr.c | 44 +++++++++++++++++++++++++++++-----------
> > 1 file changed, 32 insertions(+), 12 deletions(-)
>
> I think the patch content is fine, but please update the comments and
> the changelog to say why EFI_CONVENTIONAL_MEMORY was chosen, i.e. that
> it's the only memory type that we know to be free.
OK, I'll update this.
[toc] | [prev] | [standalone]
Back to top | Article view | linux.kernel
csiph-web