[v2] ARM: fix randomized task_struct
diff mbox

Message ID 20170630160450.4093529-1-arnd@arndb.de
State New
Headers show

Commit Message

Arnd Bergmann June 30, 2017, 4:03 p.m. UTC
With the new task struct randomization, we can run into a build
failure for certain random seeds:

arch/arm/kernel/entry-armv.S: Assembler messages:
arch/arm/kernel/entry-armv.S:803: Error: bad immediate value for offset (4096)

Only two constants in asm-offset.h are affected, and I'm changing
both of them here to work correctly in all configurations.

One more macro has the problem, but is currently unused, so this
removes it instead of adding complexity.

Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Fixes: c33d8b12fbbd ("task_struct: Allow randomized layout")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: define a more appropriate macro instead of PAGE_MASK,
    fix always-true comparison to test the right thing
---
 arch/arm/include/asm/assembler.h |  2 ++
 arch/arm/kernel/entry-armv.S     |  5 ++++-
 arch/arm/mm/proc-macros.S        | 10 ++++------
 3 files changed, 10 insertions(+), 7 deletions(-)

Comments

Kees Cook June 30, 2017, 6:27 p.m. UTC | #1
On Fri, Jun 30, 2017 at 9:03 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> With the new task struct randomization, we can run into a build
> failure for certain random seeds:
>
> arch/arm/kernel/entry-armv.S: Assembler messages:
> arch/arm/kernel/entry-armv.S:803: Error: bad immediate value for offset (4096)
>
> Only two constants in asm-offset.h are affected, and I'm changing
> both of them here to work correctly in all configurations.
>
> One more macro has the problem, but is currently unused, so this
> removes it instead of adding complexity.
>
> Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Fixes: c33d8b12fbbd ("task_struct: Allow randomized layout")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Looks great, thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

Russell, if you're happy with it can you Ack this? I'd like to carry
the change in the randstruct tree (so all the dependencies are in the
same tree).

-Kees

> ---
> v2: define a more appropriate macro instead of PAGE_MASK,
>     fix always-true comparison to test the right thing
> ---
>  arch/arm/include/asm/assembler.h |  2 ++
>  arch/arm/kernel/entry-armv.S     |  5 ++++-
>  arch/arm/mm/proc-macros.S        | 10 ++++------
>  3 files changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index 68b06f9c65de..ad301f107dd2 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -87,6 +87,8 @@
>  #define CALGN(code...)
>  #endif
>
> +#define IMM12_MASK 0xfff
> +
>  /*
>   * Enable and disable interrupts
>   */
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index 9f157e7c51e7..c731f0d2b2af 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -797,7 +797,10 @@ ENTRY(__switch_to)
>  #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
>         ldr     r7, [r2, #TI_TASK]
>         ldr     r8, =__stack_chk_guard
> -       ldr     r7, [r7, #TSK_STACK_CANARY]
> +       .if (TSK_STACK_CANARY > IMM12_MASK)
> +       add     r7, r7, #TSK_STACK_CANARY & ~IMM12_MASK
> +       .endif
> +       ldr     r7, [r7, #TSK_STACK_CANARY & IMM12_MASK]
>  #endif
>  #ifdef CONFIG_CPU_USE_DOMAINS
>         mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
> diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
> index 0d40c285bd86..f944836da8a2 100644
> --- a/arch/arm/mm/proc-macros.S
> +++ b/arch/arm/mm/proc-macros.S
> @@ -25,11 +25,6 @@
>         ldr     \rd, [\rn, #VMA_VM_FLAGS]
>         .endm
>
> -       .macro  tsk_mm, rd, rn
> -       ldr     \rd, [\rn, #TI_TASK]
> -       ldr     \rd, [\rd, #TSK_ACTIVE_MM]
> -       .endm
> -
>  /*
>   * act_mm - get current->active_mm
>   */
> @@ -37,7 +32,10 @@
>         bic     \rd, sp, #8128
>         bic     \rd, \rd, #63
>         ldr     \rd, [\rd, #TI_TASK]
> -       ldr     \rd, [\rd, #TSK_ACTIVE_MM]
> +       .if (TSK_ACTIVE_MM > IMM12_MASK)
> +       add     \rd, \rd, #TSK_ACTIVE_MM & ~IMM12_MASK
> +       .endif
> +       ldr     \rd, [\rd, #TSK_ACTIVE_MM & IMM12_MASK]
>         .endm
>
>  /*
> --
> 2.9.0
>
Kees Cook June 30, 2017, 9:54 p.m. UTC | #2
On Fri, Jun 30, 2017 at 11:27 AM, Kees Cook <keescook@chromium.org> wrote:
> On Fri, Jun 30, 2017 at 9:03 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>> With the new task struct randomization, we can run into a build
>> failure for certain random seeds:
>>
>> arch/arm/kernel/entry-armv.S: Assembler messages:
>> arch/arm/kernel/entry-armv.S:803: Error: bad immediate value for offset (4096)
>>
>> Only two constants in asm-offset.h are affected, and I'm changing
>> both of them here to work correctly in all configurations.
>>
>> One more macro has the problem, but is currently unused, so this
>> removes it instead of adding complexity.
>>
>> Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Fixes: c33d8b12fbbd ("task_struct: Allow randomized layout")
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Looks great, thanks!
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
>
> Russell, if you're happy with it can you Ack this? I'd like to carry
> the change in the randstruct tree (so all the dependencies are in the
> same tree).

I've also forced stack_canary into the end of task_struct and inflated
the size of the struct (to match randomization inflation due to
intentionally poor bitfield packing), verified the resulting .o files
have the adjustment and boot tested both cases.

Tested-by: Kees Cook <keescook@chromium.org>

-Kees

Patch
diff mbox

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 68b06f9c65de..ad301f107dd2 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -87,6 +87,8 @@ 
 #define CALGN(code...)
 #endif
 
+#define IMM12_MASK 0xfff
+
 /*
  * Enable and disable interrupts
  */
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 9f157e7c51e7..c731f0d2b2af 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -797,7 +797,10 @@  ENTRY(__switch_to)
 #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
 	ldr	r7, [r2, #TI_TASK]
 	ldr	r8, =__stack_chk_guard
-	ldr	r7, [r7, #TSK_STACK_CANARY]
+	.if (TSK_STACK_CANARY > IMM12_MASK)
+	add	r7, r7, #TSK_STACK_CANARY & ~IMM12_MASK
+	.endif
+	ldr	r7, [r7, #TSK_STACK_CANARY & IMM12_MASK]
 #endif
 #ifdef CONFIG_CPU_USE_DOMAINS
 	mcr	p15, 0, r6, c3, c0, 0		@ Set domain register
diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index 0d40c285bd86..f944836da8a2 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -25,11 +25,6 @@ 
 	ldr	\rd, [\rn, #VMA_VM_FLAGS]
 	.endm
 
-	.macro	tsk_mm, rd, rn
-	ldr	\rd, [\rn, #TI_TASK]
-	ldr	\rd, [\rd, #TSK_ACTIVE_MM]
-	.endm
-
 /*
  * act_mm - get current->active_mm
  */
@@ -37,7 +32,10 @@ 
 	bic	\rd, sp, #8128
 	bic	\rd, \rd, #63
 	ldr	\rd, [\rd, #TI_TASK]
-	ldr	\rd, [\rd, #TSK_ACTIVE_MM]
+	.if (TSK_ACTIVE_MM > IMM12_MASK)
+	add	\rd, \rd, #TSK_ACTIVE_MM & ~IMM12_MASK
+	.endif
+	ldr	\rd, [\rd, #TSK_ACTIVE_MM & IMM12_MASK]
 	.endm
 
 /*