[PATCH] x86/efi: Fix kernel panic when CONFIG_DEBUG_VIRTUAL is enabled

[PATCH] x86/efi: Fix kernel panic when CONFIG_DEBUG_VIRTUAL is enabled

[Sai Praneeth Prakhya]

From: Sai Praneeth <sai.praneeth.prakhya@intel.com>

When CONFIG_DEBUG_VIRTUAL is turned on, all accesses to __pa(address)
are monitored to see whether address falls in direct mapping or kernel
mapping, if it does not kernel panics. During 1:1 mapping of EFI runtime
services we access addresses which are below 4G and hence when passed as
arguments to __pa() kernel panics as reported by Dave Hansen here
https://lkml.org/lkml/2015/1/27/742. So, before calling __pa() virtual
addresses should be validated which results in skipping call to
split_page_count() and that should be fine because it is used to keep
track of direct kernel mappings and not 1:1 mappings.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Reported-by: Dave Hansen <dave.hansen@intel.com>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Glenn P Williamson <glenn.p.williamson@intel.com>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
---
 arch/x86/mm/pageattr.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 727158cb3b3c..3a603830503a 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -648,9 +648,11 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
 		set_pte(&pbase[i], pfn_pte(pfn, canon_pgprot(ref_prot)));
 
-	if (pfn_range_is_mapped(PFN_DOWN(__pa(address)),
-				PFN_DOWN(__pa(address)) + 1))
-		split_page_count(level);
+	if (virt_addr_valid(address)) {
+		if (pfn_range_is_mapped(PFN_DOWN(__pa(address)),
+					PFN_DOWN(__pa(address)) + 1))
+			split_page_count(level);
+	}
 
 	/*
 	 * Install the new, split up pagetable.
-- 
2.1.4

Re: [PATCH] x86/efi: Fix kernel panic when CONFIG_DEBUG_VIRTUAL is enabled

[Borislav Petkov]

On Tue, Oct 13, 2015 at 12:42:57PM -0700, Sai Praneeth Prakhya wrote:
> From: Sai Praneeth <sai.praneeth.prakhya@intel.com>
> 
> When CONFIG_DEBUG_VIRTUAL is turned on, all accesses to __pa(address)
> are monitored to see whether address falls in direct mapping or kernel
> mapping,

make that

"... or kernel text mapping (see Documentation/x86/x86_64/mm.txt for
details)"

for more clarity please. It just took mfleming and me a while to figure
out what what is.

> if it does not kernel panics. During 1:1 mapping of EFI runtime
> services we access addresses which are below 4G and hence when passed as

not "below 4G" but "we access virtual adresses which are == physical
addresses, thus the 1:1 mapping" - on a box with more than 4G, physical
addresses can be above 4G too :)

> arguments to __pa() kernel panics as reported by Dave Hansen here
> https://lkml.org/lkml/2015/1/27/742.

Please quote this mail with the k.org redirector:

https://lkml.kernel.org/r/5462999A.7090706@intel.com

lkml.org is unreliable.

> So, before calling __pa() virtual
> addresses should be validated which results in skipping call to
> split_page_count() and that should be fine because it is used to keep
> track of direct kernel mappings and not 1:1 mappings.

I think that should say:

"to keep track of everything *but* 1:1 mappings."

The 1:1 mappings are EFI-specific thing and the physaddr.c checkers
aren't aware of them.

Again, IMHO.

> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Reported-by: Dave Hansen <dave.hansen@intel.com>
> Cc: Matt Fleming <matt.fleming@intel.com>
> Cc: Ricardo Neri <ricardo.neri@intel.com>
> Cc: Glenn P Williamson <glenn.p.williamson@intel.com>
> Cc: Ravi Shankar <ravi.v.shankar@intel.com>
> ---
>  arch/x86/mm/pageattr.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 727158cb3b3c..3a603830503a 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -648,9 +648,11 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
>  	for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
>  		set_pte(&pbase[i], pfn_pte(pfn, canon_pgprot(ref_prot)));
>  
> -	if (pfn_range_is_mapped(PFN_DOWN(__pa(address)),
> -				PFN_DOWN(__pa(address)) + 1))
> -		split_page_count(level);
> +	if (virt_addr_valid(address)) {
> +		if (pfn_range_is_mapped(PFN_DOWN(__pa(address)),
> +					PFN_DOWN(__pa(address)) + 1))
> +			split_page_count(level);

Maybe make it a bit more readable:

	if (virt_addr_valid(address)) {
		unsigned long pfn = PFN_DOWN(__pa(address));

		if (pfn_range_is_mapped(pfn, pfn + 1))
			split_page_count(level);
	}


But yeah, patch makes sense to me.

Thanks for fixing that!

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

[GIT PULL] EFI changes for v4.4

[Matt Fleming]

Folks, please pull the following bugfix from Sai which prevents a
kernel panic when booting an EFI machine with CONFIG_DEBUG_VIRTUAL
enabled.

This bug was reported last year by Dave Hansen,

  https://lkml.kernel.org/r/5462999A.7090706@intel.com

and since nobody else has reported it, and given that it's only
triggerable with a debug config option, I figured this should be
targeted at v4.4.

The following changes since commit 0f96a99dab366333439e110d6ad253bc7c557c09:

  efi: Add "efi_fake_mem" boot option (2015-10-12 14:20:09 +0100)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/mfleming/efi.git tags/efi-next

for you to fetch changes up to 2c66e24d75d424919c42288b418d2e593fa818b1:

  x86/efi: Fix kernel panic when CONFIG_DEBUG_VIRTUAL is enabled (2015-10-25 10:22:25 +0000)

----------------------------------------------------------------
 * Fix a kernel panic by not passing EFI virtual mapping addresses to
   __pa() in the x86 pageattr code. Since these virtual addreses are
  not part of the direct mapping or kernel text mapping, passing them
  to __pa() will trigger a BUG_ON() when CONFIG_DEBUG_VIRTUAL is
  enabled - Sai Praneeth Prakhya

----------------------------------------------------------------
Sai Praneeth (1):
      x86/efi: Fix kernel panic when CONFIG_DEBUG_VIRTUAL is enabled

 arch/x86/mm/pageattr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

[PATCH] x86/efi: Fix kernel panic when CONFIG_DEBUG_VIRTUAL is enabled

[Matt Fleming]

From: Sai Praneeth <sai.praneeth.prakhya@intel.com>

When CONFIG_DEBUG_VIRTUAL is enabled, all accesses to __pa(address) are
monitored to see whether address falls in direct mapping or kernel text
mapping (see Documentation/x86/x86_64/mm.txt for details), if it does
not, the kernel panics. During 1:1 mapping of EFI runtime services we access
virtual addresses which are == physical addresses, thus the 1:1 mapping
and these addresses do not fall in either of the above two regions and
hence when passed as arguments to __pa() kernel panics as reported by
Dave Hansen here https://lkml.kernel.org/r/5462999A.7090706@intel.com.

So, before calling __pa() virtual addresses should be validated which
results in skipping call to split_page_count() and that should be fine
because it is used to keep track of everything *but* 1:1 mappings.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Reported-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Glenn P Williamson <glenn.p.williamson@intel.com>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
---
 arch/x86/mm/pageattr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 727158cb3b3c..9abe0c9b1098 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -648,9 +648,12 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
 		set_pte(&pbase[i], pfn_pte(pfn, canon_pgprot(ref_prot)));
 
-	if (pfn_range_is_mapped(PFN_DOWN(__pa(address)),
-				PFN_DOWN(__pa(address)) + 1))
-		split_page_count(level);
+	if (virt_addr_valid(address)) {
+		unsigned long pfn = PFN_DOWN(__pa(address));
+
+		if (pfn_range_is_mapped(pfn, pfn + 1))
+			split_page_count(level);
+	}
 
 	/*
 	 * Install the new, split up pagetable.
-- 
2.6.0