linux-kernel - [tip:efi/core] efi/libstub/arm: Don't use TASK

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Date:   Tue, 18 Apr 2017 00:25:14 -0700
From:   tip-bot for Ard Biesheuvel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, hpa@...or.com, tglx@...utronix.de,
        james.morse@....com, matt@...eblueprint.co.uk, mingo@...nel.org,
        catalin.marinas@....com, mark.rutland@....com,
        linux-kernel@...r.kernel.org, ard.biesheuvel@...aro.org,
        torvalds@...ux-foundation.org
Subject: [tip:efi/core] efi/libstub/arm: Don't use TASK_SIZE when
 randomizing the RT space

Commit-ID:  197decefdb79d6f1350ba0316ce26ba737372d0c
Gitweb:     http://git.kernel.org/tip/197decefdb79d6f1350ba0316ce26ba737372d0c
Author:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
AuthorDate: Mon, 17 Apr 2017 10:32:01 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
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 <mark.rutland@....com>
Tested-by: James Morse <james.morse@....com>
Tested-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-efi@...r.kernel.org
Link: http://lkml.kernel.org/r/20170417093201.10181-2-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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_BASE	SZ_512M
 #define EFI_RT_VIRTUAL_SIZE	SZ_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),