[PATCH 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[PATCH 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[Jiri Slaby]

Non-PAE 32-bit dump kernels may wrap an address around 4G and
poke unwanted space. ptes there are 32-bit long, and since
pfn << PAGE_SIZE may exceed this limit, high pfn bits are cropped
and wrong address mapped by kmap_atomic_pfn in copy_oldmem_page.

Don't allow this behavior in non-PAE kdump kernels by checking
pfns passed into copy_oldmem_page. In the case of failure,
userspace process gets EFAULT.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/crash_dump_32.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
index f7cdb3b..b78dab8 100644
--- a/arch/x86/kernel/crash_dump_32.c
+++ b/arch/x86/kernel/crash_dump_32.c
@@ -16,6 +16,19 @@ static void *kdump_buf_page;
 /* Stores the physical address of elf header of crash image. */
 unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
 
+#ifndef CONFIG_X86_PAE
+/* non-PAE kdump kernel executed from a PAE one will crop high pte bits and
+   poke unwanted space counting again from address 0, we don't want that */
+static inline bool is_crashed_pfn_valid(unsigned long pfn)
+{
+	/* on non-PAE pte must fit into unsigned long
+	   in fact the test is (pfn & 0x000fffff) */
+	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
+}
+#else
+static inline bool is_crashed_pfn_valid(unsigned long pfn) { return true; }
+#endif
+
 /**
  * copy_oldmem_page - copy one page from "oldmem"
  * @pfn: page frame number to be copied
@@ -41,6 +54,9 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!csize)
 		return 0;
 
+	if (!is_crashed_pfn_valid(pfn))
+		return -EFAULT;
+
 	vaddr = kmap_atomic_pfn(pfn, KM_PTE0);
 
 	if (!userbuf) {
-- 
1.6.4.2

Re: [PATCH 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[Ingo Molnar]

* Jiri Slaby <jirislaby@gmail.com> wrote:

> Non-PAE 32-bit dump kernels may wrap an address around 4G and
> poke unwanted space. ptes there are 32-bit long, and since
> pfn << PAGE_SIZE may exceed this limit, high pfn bits are cropped
> and wrong address mapped by kmap_atomic_pfn in copy_oldmem_page.
> 
> Don't allow this behavior in non-PAE kdump kernels by checking
> pfns passed into copy_oldmem_page. In the case of failure,
> userspace process gets EFAULT.
> 
> Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Simon Horman <horms@verge.net.au>
> Cc: Paul Mundt <lethal@linux-sh.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
>  arch/x86/kernel/crash_dump_32.c |   16 ++++++++++++++++
>  1 files changed, 16 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
> index f7cdb3b..b78dab8 100644
> --- a/arch/x86/kernel/crash_dump_32.c
> +++ b/arch/x86/kernel/crash_dump_32.c
> @@ -16,6 +16,19 @@ static void *kdump_buf_page;
>  /* Stores the physical address of elf header of crash image. */
>  unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
>  
> +#ifndef CONFIG_X86_PAE
> +/* non-PAE kdump kernel executed from a PAE one will crop high pte bits and
> +   poke unwanted space counting again from address 0, we don't want that */
> +static inline bool is_crashed_pfn_valid(unsigned long pfn)
> +{
> +	/* on non-PAE pte must fit into unsigned long
> +	   in fact the test is (pfn & 0x000fffff) */
> +	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
> +}
> +#else
> +static inline bool is_crashed_pfn_valid(unsigned long pfn) { return true; }
> +#endif

i'd suggest to push the #ifdef inside the function.

Also, please use the customary (multi-line) comment style:

  /*
   * Comment .....
   * ...... goes here.
   */

specified in Documentation/CodingStyle.

Thanks,

        Ingo

[PATCH v2 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[Jiri Slaby]

Non-PAE 32-bit dump kernels may wrap an address around 4G and
poke unwanted space. ptes there are 32-bit long, and since
pfn << PAGE_SIZE may exceed this limit, high pfn bits are cropped
and wrong address mapped by kmap_atomic_pfn in copy_oldmem_page.

Don't allow this behavior in non-PAE kdump kernels by checking
pfns passed into copy_oldmem_page. In the case of failure,
userspace process gets EFAULT.

[v2]
- fix comments
- move ifdefs inside the function

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/crash_dump_32.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
index f7cdb3b..cd97ce1 100644
--- a/arch/x86/kernel/crash_dump_32.c
+++ b/arch/x86/kernel/crash_dump_32.c
@@ -16,6 +16,22 @@ static void *kdump_buf_page;
 /* Stores the physical address of elf header of crash image. */
 unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
 
+static inline bool is_crashed_pfn_valid(unsigned long pfn)
+{
+#ifndef CONFIG_X86_PAE
+	/*
+	 * non-PAE kdump kernel executed from a PAE one will crop high pte
+	 * bits and poke unwanted space counting again from address 0, we
+	 * don't want that. pte must fit into unsigned long. In fact the
+	 * test checks high 12 bits for being zero (pfn will be shifted left
+	 * by PAGE_SHIFT).
+	 */
+	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
+#else
+	return true;
+#endif
+}
+
 /**
  * copy_oldmem_page - copy one page from "oldmem"
  * @pfn: page frame number to be copied
@@ -41,6 +57,9 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!csize)
 		return 0;
 
+	if (!is_crashed_pfn_valid(pfn))
+		return -EFAULT;
+
 	vaddr = kmap_atomic_pfn(pfn, KM_PTE0);
 
 	if (!userbuf) {
-- 
1.6.4.2

Re: [PATCH 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[Jiri Slaby]

On 10/25/2009 05:20 PM, Ingo Molnar wrote:
>> +#ifndef CONFIG_X86_PAE
>> +/* non-PAE kdump kernel executed from a PAE one will crop high pte bits and
>> +   poke unwanted space counting again from address 0, we don't want that */
>> +static inline bool is_crashed_pfn_valid(unsigned long pfn)
>> +{
>> +	/* on non-PAE pte must fit into unsigned long
>> +	   in fact the test is (pfn & 0x000fffff) */
>> +	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
>> +}
>> +#else
>> +static inline bool is_crashed_pfn_valid(unsigned long pfn) { return true; }
>> +#endif
> 
> i'd suggest to push the #ifdef inside the function.

I posted a v2 patch a second ago. Thanks.

[tip:x86/urgent] x86: crash_dump: Fix non-pae kdump kernel memory accesses

[tip-bot for Jiri Slaby]

Commit-ID:  72ed7de74e8f0fad0d8e567ae1f987b740accb3f
Gitweb:     http://git.kernel.org/tip/72ed7de74e8f0fad0d8e567ae1f987b740accb3f
Author:     Jiri Slaby <jirislaby@gmail.com>
AuthorDate: Mon, 26 Oct 2009 11:11:43 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 26 Oct 2009 12:38:59 +0100

x86: crash_dump: Fix non-pae kdump kernel memory accesses

Non-PAE 32-bit dump kernels may wrap an address around 4G and
poke unwanted space. ptes there are 32-bit long, and since
pfn << PAGE_SIZE may exceed this limit, high pfn bits are
cropped and wrong address mapped by kmap_atomic_pfn in
copy_oldmem_page.

Don't allow this behavior in non-PAE kdump kernels by checking
pfns passed into copy_oldmem_page. In the case of failure,
userspace process gets EFAULT.

[v2]
- fix comments
- move ifdefs inside the function

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Paul Mundt <lethal@linux-sh.org>
LKML-Reference: <1256551903-30567-1-git-send-email-jirislaby@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/crash_dump_32.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
index f7cdb3b..cd97ce1 100644
--- a/arch/x86/kernel/crash_dump_32.c
+++ b/arch/x86/kernel/crash_dump_32.c
@@ -16,6 +16,22 @@ static void *kdump_buf_page;
 /* Stores the physical address of elf header of crash image. */
 unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
 
+static inline bool is_crashed_pfn_valid(unsigned long pfn)
+{
+#ifndef CONFIG_X86_PAE
+	/*
+	 * non-PAE kdump kernel executed from a PAE one will crop high pte
+	 * bits and poke unwanted space counting again from address 0, we
+	 * don't want that. pte must fit into unsigned long. In fact the
+	 * test checks high 12 bits for being zero (pfn will be shifted left
+	 * by PAGE_SHIFT).
+	 */
+	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
+#else
+	return true;
+#endif
+}
+
 /**
  * copy_oldmem_page - copy one page from "oldmem"
  * @pfn: page frame number to be copied
@@ -41,6 +57,9 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!csize)
 		return 0;
 
+	if (!is_crashed_pfn_valid(pfn))
+		return -EFAULT;
+
 	vaddr = kmap_atomic_pfn(pfn, KM_PTE0);
 
 	if (!userbuf) {

Re: [PATCH v2 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[Eric W. Biederman]

Jiri Slaby <jirislaby@gmail.com> writes:

> Non-PAE 32-bit dump kernels may wrap an address around 4G and
> poke unwanted space. ptes there are 32-bit long, and since
> pfn << PAGE_SIZE may exceed this limit, high pfn bits are cropped
> and wrong address mapped by kmap_atomic_pfn in copy_oldmem_page.
>
> Don't allow this behavior in non-PAE kdump kernels by checking
> pfns passed into copy_oldmem_page. In the case of failure,
> userspace process gets EFAULT.

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

Looks good to me.

> [v2]
> - fix comments
> - move ifdefs inside the function
>
> Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Simon Horman <horms@verge.net.au>
> Cc: Paul Mundt <lethal@linux-sh.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
>  arch/x86/kernel/crash_dump_32.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
> index f7cdb3b..cd97ce1 100644
> --- a/arch/x86/kernel/crash_dump_32.c
> +++ b/arch/x86/kernel/crash_dump_32.c
> @@ -16,6 +16,22 @@ static void *kdump_buf_page;
>  /* Stores the physical address of elf header of crash image. */
>  unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
>  
> +static inline bool is_crashed_pfn_valid(unsigned long pfn)
> +{
> +#ifndef CONFIG_X86_PAE
> +	/*
> +	 * non-PAE kdump kernel executed from a PAE one will crop high pte
> +	 * bits and poke unwanted space counting again from address 0, we
> +	 * don't want that. pte must fit into unsigned long. In fact the
> +	 * test checks high 12 bits for being zero (pfn will be shifted left
> +	 * by PAGE_SHIFT).
> +	 */
> +	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
> +#else
> +	return true;
> +#endif
> +}
> +
>  /**
>   * copy_oldmem_page - copy one page from "oldmem"
>   * @pfn: page frame number to be copied
> @@ -41,6 +57,9 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
>  	if (!csize)
>  		return 0;
>  
> +	if (!is_crashed_pfn_valid(pfn))
> +		return -EFAULT;
> +
>  	vaddr = kmap_atomic_pfn(pfn, KM_PTE0);
>  
>  	if (!userbuf) {
> -- 
> 1.6.4.2

Re: [PATCH v2 1/1] crash_dump: fix non-pae kdump kernel memory accesses

[Vivek Goyal]

On Mon, Oct 26, 2009 at 11:11:43AM +0100, Jiri Slaby wrote:
> Non-PAE 32-bit dump kernels may wrap an address around 4G and
> poke unwanted space. ptes there are 32-bit long, and since
> pfn << PAGE_SIZE may exceed this limit, high pfn bits are cropped
> and wrong address mapped by kmap_atomic_pfn in copy_oldmem_page.
> 
> Don't allow this behavior in non-PAE kdump kernels by checking
> pfns passed into copy_oldmem_page. In the case of failure,
> userspace process gets EFAULT.
> 
> [v2]
> - fix comments
> - move ifdefs inside the function
> 
> Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Simon Horman <horms@verge.net.au>
> Cc: Paul Mundt <lethal@linux-sh.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---

Looks good to me.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Thanks
Vivek

>  arch/x86/kernel/crash_dump_32.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash_dump_32.c b/arch/x86/kernel/crash_dump_32.c
> index f7cdb3b..cd97ce1 100644
> --- a/arch/x86/kernel/crash_dump_32.c
> +++ b/arch/x86/kernel/crash_dump_32.c
> @@ -16,6 +16,22 @@ static void *kdump_buf_page;
>  /* Stores the physical address of elf header of crash image. */
>  unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
>  
> +static inline bool is_crashed_pfn_valid(unsigned long pfn)
> +{
> +#ifndef CONFIG_X86_PAE
> +	/*
> +	 * non-PAE kdump kernel executed from a PAE one will crop high pte
> +	 * bits and poke unwanted space counting again from address 0, we
> +	 * don't want that. pte must fit into unsigned long. In fact the
> +	 * test checks high 12 bits for being zero (pfn will be shifted left
> +	 * by PAGE_SHIFT).
> +	 */
> +	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
> +#else
> +	return true;
> +#endif
> +}
> +
>  /**
>   * copy_oldmem_page - copy one page from "oldmem"
>   * @pfn: page frame number to be copied
> @@ -41,6 +57,9 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
>  	if (!csize)
>  		return 0;
>  
> +	if (!is_crashed_pfn_valid(pfn))
> +		return -EFAULT;
> +
>  	vaddr = kmap_atomic_pfn(pfn, KM_PTE0);
>  
>  	if (!userbuf) {
> -- 
> 1.6.4.2