[tip:efi/core] efi/libstub/arm: Don't use TASK_SIZE when randomizing the RT space

[tip-bot for Ard Biesheuvel]

Commit-ID:  197decefdb79d6f1350ba0316ce26ba737372d0c
Gitweb: http://git.kernel.org/tip/197decefdb79d6f1350ba0316ce26ba737372d0c
Author: Ard Biesheuvel 
AuthorDate: Mon, 17 Apr 2017 10:32:01 +0100
Committer:  Ingo Molnar 
CommitDate: Mon, 17 Apr 2017 12:35:33 +0200

efi/libstub/arm: Don't use TASK_SIZE when randomizing the RT space

As reported by James, Catalin and Mark, commit:

  e69176d68d26 ("ef/libstub/arm/arm64: Randomize the base of the UEFI rt 
services region")

... results in a crash in the firmware, regardless of whether KASLR
is in effect or not and whether the firmware implements EFI_RNG_PROTOCOL
or not.

Mark has identified the root cause to be the inappropriate use of
TASK_SIZE in the stub, which arm64 defines as:

  #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)

and testing thread flags at this point results in the dereference of
pointers in uninitialized structures.

So instead, introduce a preprocessor symbol EFI_RT_VIRTUAL_LIMIT and
define it to TASK_SIZE_64 on arm64 and TASK_SIZE on ARM, both of which
are compile time constants. Also, change the 'headroom' variable to
static const to force an error if this might change in the future.

Tested-by: Mark Rutland 
Tested-by: James Morse 
Tested-by: Catalin Marinas 
Signed-off-by: Ard Biesheuvel 
Cc: Linus Torvalds 
Cc: Matt Fleming 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-...@vger.kernel.org
Link: http://lkml.kernel.org/r/20170417093201.10181-2-ard.biesheu...@linaro.org
Signed-off-by: Ingo Molnar 
---
 drivers/firmware/efi/libstub/arm-stub.c | 11 +--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/libstub/arm-stub.c 
b/drivers/firmware/efi/libstub/arm-stub.c
index 1e45ec5..8181ac1 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -32,6 +32,12 @@
 #define EFI_RT_VIRTUAL_BASESZ_512M
 #define EFI_RT_VIRTUAL_SIZESZ_512M
 
+#ifdef CONFIG_ARM64
+# define EFI_RT_VIRTUAL_LIMIT  TASK_SIZE_64
+#else
+# define EFI_RT_VIRTUAL_LIMIT  TASK_SIZE
+#endif
+
 static u64 virtmap_base = EFI_RT_VIRTUAL_BASE;
 
 efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg,
@@ -236,8 +242,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t 
*sys_table,
 * shift of 21 bit positions into account when scaling
 * the headroom value using a 32-bit random value.
 */
-   u64 headroom = TASK_SIZE - EFI_RT_VIRTUAL_BASE -
-  EFI_RT_VIRTUAL_SIZE;
+   static const u64 headroom = EFI_RT_VIRTUAL_LIMIT -
+   EFI_RT_VIRTUAL_BASE -
+   EFI_RT_VIRTUAL_SIZE;
u32 rnd;
 
status = efi_get_random_bytes(sys_table, sizeof(rnd),

[tip:efi/core] efi/libstub/arm: Don't use TASK_SIZE when randomizing the RT space

[tip-bot for Ard Biesheuvel]

Commit-ID:  197decefdb79d6f1350ba0316ce26ba737372d0c
Gitweb: http://git.kernel.org/tip/197decefdb79d6f1350ba0316ce26ba737372d0c
Author: Ard Biesheuvel 
AuthorDate: Mon, 17 Apr 2017 10:32:01 +0100
Committer:  Ingo Molnar 
CommitDate: Mon, 17 Apr 2017 12:35:33 +0200

efi/libstub/arm: Don't use TASK_SIZE when randomizing the RT space

As reported by James, Catalin and Mark, commit:

  e69176d68d26 ("ef/libstub/arm/arm64: Randomize the base of the UEFI rt 
services region")

... results in a crash in the firmware, regardless of whether KASLR
is in effect or not and whether the firmware implements EFI_RNG_PROTOCOL
or not.

Mark has identified the root cause to be the inappropriate use of
TASK_SIZE in the stub, which arm64 defines as:

  #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)

and testing thread flags at this point results in the dereference of
pointers in uninitialized structures.

So instead, introduce a preprocessor symbol EFI_RT_VIRTUAL_LIMIT and
define it to TASK_SIZE_64 on arm64 and TASK_SIZE on ARM, both of which
are compile time constants. Also, change the 'headroom' variable to
static const to force an error if this might change in the future.

Tested-by: Mark Rutland 
Tested-by: James Morse 
Tested-by: Catalin Marinas 
Signed-off-by: Ard Biesheuvel 
Cc: Linus Torvalds 
Cc: Matt Fleming 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-...@vger.kernel.org
Link: http://lkml.kernel.org/r/20170417093201.10181-2-ard.biesheu...@linaro.org
Signed-off-by: Ingo Molnar 
---
 drivers/firmware/efi/libstub/arm-stub.c | 11 +--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/libstub/arm-stub.c 
b/drivers/firmware/efi/libstub/arm-stub.c
index 1e45ec5..8181ac1 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -32,6 +32,12 @@
 #define EFI_RT_VIRTUAL_BASESZ_512M
 #define EFI_RT_VIRTUAL_SIZESZ_512M
 
+#ifdef CONFIG_ARM64
+# define EFI_RT_VIRTUAL_LIMIT  TASK_SIZE_64
+#else
+# define EFI_RT_VIRTUAL_LIMIT  TASK_SIZE
+#endif
+
 static u64 virtmap_base = EFI_RT_VIRTUAL_BASE;
 
 efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg,
@@ -236,8 +242,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t 
*sys_table,
 * shift of 21 bit positions into account when scaling
 * the headroom value using a 32-bit random value.
 */
-   u64 headroom = TASK_SIZE - EFI_RT_VIRTUAL_BASE -
-  EFI_RT_VIRTUAL_SIZE;
+   static const u64 headroom = EFI_RT_VIRTUAL_LIMIT -
+   EFI_RT_VIRTUAL_BASE -
+   EFI_RT_VIRTUAL_SIZE;
u32 rnd;
 
status = efi_get_random_bytes(sys_table, sizeof(rnd),