* [PATCH v2] ARM: fix randomized task_struct
@ 2017-06-30 16:03 Arnd Bergmann
2017-06-30 18:27 ` Kees Cook
0 siblings, 1 reply; 3+ messages in thread
From: Arnd Bergmann @ 2017-06-30 16:03 UTC (permalink / raw)
To: Kees Cook
Cc: kernel-hardening, Arnd Bergmann, Russell King, Will Deacon,
linux-arm-kernel, linux-kernel
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(-)
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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v2] ARM: fix randomized task_struct
2017-06-30 16:03 [PATCH v2] ARM: fix randomized task_struct Arnd Bergmann
@ 2017-06-30 18:27 ` Kees Cook
2017-06-30 21:54 ` Kees Cook
0 siblings, 1 reply; 3+ messages in thread
From: Kees Cook @ 2017-06-30 18:27 UTC (permalink / raw)
To: Arnd Bergmann
Cc: kernel-hardening, Russell King, Will Deacon, linux-arm-kernel, LKML
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
Pixel Security
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v2] ARM: fix randomized task_struct
2017-06-30 18:27 ` Kees Cook
@ 2017-06-30 21:54 ` Kees Cook
0 siblings, 0 replies; 3+ messages in thread
From: Kees Cook @ 2017-06-30 21:54 UTC (permalink / raw)
To: Arnd Bergmann
Cc: kernel-hardening, Russell King, Will Deacon, linux-arm-kernel, LKML
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
--
Kees Cook
Pixel Security
^ permalink raw reply [flat|nested] 3+ messages in thread
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