[4.4] broken conversion from efi to kernel page table

[4.4] broken conversion from efi to kernel page table

[Pavel Tatashin]

This fixes boot panics, hangs which I reported in this thread:

http://lkml.iu.edu/hypermail/linux/kernel/1801.1/00951.html

I have not yet verified if similar issue is applicable to newer
kernels.

Re-sending it as a proper git send-email submission.

Pavel Tatashin (1):
  x86/pti/efi: broken conversion from efi to kernel page table

 arch/x86/include/asm/kaiser.h        | 8 ++++++++
 arch/x86/realmode/init.c             | 4 +++-
 arch/x86/realmode/rm/trampoline_64.S | 3 ++-
 3 files changed, 13 insertions(+), 2 deletions(-)

-- 
1.8.3.1

[4.4] x86/pti/efi: broken conversion from efi to kernel page table

[Pavel Tatashin]

In entry_64.S we have code like this:

    /* Unconditionally use kernel CR3 for do_nmi() */
    /* %rax is saved above, so OK to clobber here */
    ALTERNATIVE "jmp 2f", "movq %cr3, %rax", X86_FEATURE_KAISER
    /* If PCID enabled, NOFLUSH now and NOFLUSH on return */
    ALTERNATIVE "", "bts $63, %rax", X86_FEATURE_PCID
    pushq   %rax
    /* mask off "user" bit of pgd address and 12 PCID bits: */
    andq    $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), %rax
    movq    %rax, %cr3
2:

    /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
    call    do_nmi

With this instruction:
    andq    $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), %rax

We unconditionally switch from whatever our CR3 was to kernel page table.
But, in arch/x86/platform/efi/efi_64.c We temporarily set a different page
table, that does not have the kernel page table with 0x1000 offset from it.

Look in efi_thunk() and efi_thunk_set_virtual_address_map().

So, while CR3 points to the other page table, we get an NMI interrupt,
and clear 0x1000 from CR3, resulting in a bogus CR3 if the 0x1000 bit was
set.

The efi page table comes from realmode/rm/trampoline_64.S:

arch/x86/realmode/rm/trampoline_64.S

141 .bss
142 .balign PAGE_SIZE
143 GLOBAL(trampoline_pgd) .space PAGE_SIZE

Notice: alignment is PAGE_SIZE, so after applying KAISER_SHADOW_PGD_OFFSET
which equal to PAGE_SIZE, we can get a different page table.

But, even if we fix alignment, here the trampoline binary is later copied
into dynamically allocated memory in reserve_real_mode(), so we need to
fix that place as well.

Fixes: 8a43ddfb93a0 ("KAISER: Kernel Address Isolation")

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
---
 arch/x86/include/asm/kaiser.h        | 8 ++++++++
 arch/x86/realmode/init.c             | 4 +++-
 arch/x86/realmode/rm/trampoline_64.S | 3 ++-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kaiser.h b/arch/x86/include/asm/kaiser.h
index 802bbbdfe143..e087bd7a8d29 100644
--- a/arch/x86/include/asm/kaiser.h
+++ b/arch/x86/include/asm/kaiser.h
@@ -19,6 +19,12 @@
 
 #define KAISER_SHADOW_PGD_OFFSET 0x1000
 
+/*
+ *  A page table address must have this alignment to stay the same when
+ *  KAISER_SHADOW_PGD_OFFSET mask is applied
+ */
+#define KAISER_KERNEL_PGD_ALIGNMENT (KAISER_SHADOW_PGD_OFFSET << 1)
+
 #ifdef __ASSEMBLY__
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
 
@@ -71,6 +77,8 @@ movq PER_CPU_VAR(unsafe_stack_register_backup), %rax
 
 #else /* CONFIG_PAGE_TABLE_ISOLATION */
 
+#define KAISER_KERNEL_PGD_ALIGNMENT PAGE_SIZE
+
 .macro SWITCH_KERNEL_CR3
 .endm
 .macro SWITCH_USER_CR3
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 0b7a63d98440..cfecb7d6c6a8 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -1,5 +1,6 @@
 #include <linux/io.h>
 #include <linux/memblock.h>
+#include <linux/kaiser.h>
 
 #include <asm/cacheflush.h>
 #include <asm/pgtable.h>
@@ -15,7 +16,8 @@ void __init reserve_real_mode(void)
 	size_t size = PAGE_ALIGN(real_mode_blob_end - real_mode_blob);
 
 	/* Has to be under 1M so we can execute real-mode AP code. */
-	mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
+	mem = memblock_find_in_range(0, 1 << 20, size,
+				     KAISER_KERNEL_PGD_ALIGNMENT);
 	if (!mem)
 		panic("Cannot allocate trampoline\n");
 
diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
index dac7b20d2f9d..781cca63f795 100644
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -30,6 +30,7 @@
 #include <asm/msr.h>
 #include <asm/segment.h>
 #include <asm/processor-flags.h>
+#include <asm/kaiser.h>
 #include "realmode.h"
 
 	.text
@@ -139,7 +140,7 @@ tr_gdt:
 tr_gdt_end:
 
 	.bss
-	.balign	PAGE_SIZE
+	.balign	KAISER_KERNEL_PGD_ALIGNMENT
 GLOBAL(trampoline_pgd)		.space	PAGE_SIZE
 
 	.balign	8
-- 
1.8.3.1

Re: [4.4] broken conversion from efi to kernel page table

[Jiri Kosina]

On Thu, 11 Jan 2018, Pavel Tatashin wrote:

> This fixes boot panics, hangs which I reported in this thread:

Are you using EFI old_memmap?

If so, then

	https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/pti&id=de53c3786a3ce162a1c815d0c04c766c23ec9c0a

("x86/pti: Unbreak EFI old_memmap") should be the cure.

If not, you might be missing this in in arch/x86/platform/efi/efi_64.c

-      efi_pgd = (pgd_t *)__get_free_page(gfp_mask);
+      efi_pgd = (pgd_t *)__get_free_pages(gfp_mask, PGD_ALLOCATION_ORDER);

Could you please let me know if either of this fixes your problem?

Thanks,

-- 
Jiri Kosina
SUSE Labs

Re: [4.4] broken conversion from efi to kernel page table

[Pavel Tatashin]

Hi Jiri,

This patch solves a different problem than _PAGE_NX. The problem it
solves is similar to
+      efi_pgd = (pgd_t *)__get_free_pages(gfp_mask,
PGD_ALLOCATION_ORDER);, Where after applying PTI mask CR3 can point to
invalid page table.
But, this patch is specific to stable 4.4.110 since it uses
trampoline_pgd from realmode, instead of allocating its own page table
as 4.6 and later do.

Thank you,
Pavel

On Fri, Jan 12, 2018 at 5:04 AM, Jiri Kosina <jikos@kernel.org> wrote:
> On Thu, 11 Jan 2018, Pavel Tatashin wrote:
>
>> This fixes boot panics, hangs which I reported in this thread:
>
> Are you using EFI old_memmap?
>
> If so, then
>
>         https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/pti&id=de53c3786a3ce162a1c815d0c04c766c23ec9c0a
>
> ("x86/pti: Unbreak EFI old_memmap") should be the cure.
>
> If not, you might be missing this in in arch/x86/platform/efi/efi_64.c
>
> -      efi_pgd = (pgd_t *)__get_free_page(gfp_mask);
> +      efi_pgd = (pgd_t *)__get_free_pages(gfp_mask, PGD_ALLOCATION_ORDER);
>
> Could you please let me know if either of this fixes your problem?
>
> Thanks,
>
> --
> Jiri Kosina
> SUSE Labs
>

Re: [4.4] broken conversion from efi to kernel page table

[Greg KH]

On Thu, Jan 11, 2018 at 02:07:45PM -0500, Pavel Tatashin wrote:
> This fixes boot panics, hangs which I reported in this thread:
> 
> http://lkml.iu.edu/hypermail/linux/kernel/1801.1/00951.html
> 
> I have not yet verified if similar issue is applicable to newer
> kernels.
> 
> Re-sending it as a proper git send-email submission.
> 
> Pavel Tatashin (1):
>   x86/pti/efi: broken conversion from efi to kernel page table
> 
>  arch/x86/include/asm/kaiser.h        | 8 ++++++++
>  arch/x86/realmode/init.c             | 4 +++-
>  arch/x86/realmode/rm/trampoline_64.S | 3 ++-
>  3 files changed, 13 insertions(+), 2 deletions(-)

Many thanks for this work, and the patch, it's greatly appreciated.

Now queued up, thanks.

greg k-h

Re: [4.4] broken conversion from efi to kernel page table

[Pavel Tatashin]

Hi Greg,

Make sure you apply:
[PATCH 4.4 v2] x86/pti/efi: broken conversion from efi to kernel page table

It is the same patch but fixes a compiling issue when compiled
without: CONFIG_PAGE_TABLE_ISOLATION


On Sat, Jan 13, 2018 at 8:18 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Thu, Jan 11, 2018 at 02:07:45PM -0500, Pavel Tatashin wrote:
>> This fixes boot panics, hangs which I reported in this thread:
>>
>> http://lkml.iu.edu/hypermail/linux/kernel/1801.1/00951.html
>>
>> I have not yet verified if similar issue is applicable to newer
>> kernels.
>>
>> Re-sending it as a proper git send-email submission.
>>
>> Pavel Tatashin (1):
>>   x86/pti/efi: broken conversion from efi to kernel page table
>>
>>  arch/x86/include/asm/kaiser.h        | 8 ++++++++
>>  arch/x86/realmode/init.c             | 4 +++-
>>  arch/x86/realmode/rm/trampoline_64.S | 3 ++-
>>  3 files changed, 13 insertions(+), 2 deletions(-)
>
> Many thanks for this work, and the patch, it's greatly appreciated.
>
> Now queued up, thanks.
>
> greg k-h

Re: [4.4] broken conversion from efi to kernel page table

[Greg KH]

On Sat, Jan 13, 2018 at 08:35:05AM -0500, Pavel Tatashin wrote:
> Hi Greg,
> 
> Make sure you apply:
> [PATCH 4.4 v2] x86/pti/efi: broken conversion from efi to kernel page table
> 
> It is the same patch but fixes a compiling issue when compiled
> without: CONFIG_PAGE_TABLE_ISOLATION

Ah, thanks, now fixed up.

In the future, any stable patches should be at least cc:
stable@vger.kernel.org, which is why I missed the v2 as it was burried
in my inbox.  I'm still trying to dig all of the crap out of there at
the moment, it's a mess...

thanks again,

greg k-h