[PATCH RFC] powerpc/32: fix handling of stack protector with recent GCC

From: Christophe Leroy
Date: Mon Jan 16 2017 - 04:00:39 EST

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Since 2005, powerpc GCC doesn't manage anymore __stack_chk_guard as
a global variable but as some value located at -0x7008(r2)

In the Linux kernel, r2 is used as a pointer to current task struct.

This patch changes the meaning of r2 when stack protector
is activated:
- current is taken from thread_info and not kept in r2 anymore
- r2 is set to current + offset of stack canary + 0x7008 so
that -0x7008(r2) directly points to current->stack_canary

current could have been more efficiently calculated from r2
but some circular inclusion prevent inserting struct task_struct
into arch/powerpc/include/asm/current.h so it is not possible
to get offset of stack_canary within current task_struct from there.

fixes: 6533b7c16ee57 ("powerpc: Initial stack protector
(-fstack-protector) support")
Reported-by: Christian Kujau <lists@xxxxxxxxxxxxxxx>

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
Christian, can you test it ?

arch/powerpc/include/asm/current.h | 12 +++++++++++-
arch/powerpc/include/asm/stackprotector.h | 13 +++++++++----
arch/powerpc/kernel/entry_32.S | 19 +++++++++++++++----
arch/powerpc/kernel/head_32.S | 7 +++++++
arch/powerpc/kernel/head_40x.S | 4 ++++
arch/powerpc/kernel/head_44x.S | 4 ++++
arch/powerpc/kernel/head_8xx.S | 4 ++++
arch/powerpc/kernel/head_fsl_booke.S | 7 +++++++
arch/powerpc/kernel/process.c | 6 ------
9 files changed, 61 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/current.h b/arch/powerpc/include/asm/current.h
index e2c7f06..2f67f02 100644
--- a/arch/powerpc/include/asm/current.h
+++ b/arch/powerpc/include/asm/current.h
@@ -27,8 +27,16 @@ static inline struct task_struct *get_current(void)
}
#define current get_current()

-#else
+#else /* __powerpc64__ */
+#if defined(CONFIG_CC_STACKPROTECTOR)
+#include <linux/thread_info.h>

+static inline struct task_struct *get_current(void)
+{
+ return current_thread_info()->task;
+}
+#define current get_current()
+#else
/*
* We keep `current' in r2 for speed.
*/
@@ -36,5 +44,7 @@ register struct task_struct *current asm ("r2");

#endif

+#endif /* __powerpc64__ */
+
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_CURRENT_H */
diff --git a/arch/powerpc/include/asm/stackprotector.h b/arch/powerpc/include/asm/stackprotector.h
index 6720190..bf30509 100644
--- a/arch/powerpc/include/asm/stackprotector.h
+++ b/arch/powerpc/include/asm/stackprotector.h
@@ -12,12 +12,18 @@
#ifndef _ASM_STACKPROTECTOR_H
#define _ASM_STACKPROTECTOR_H

+#ifdef CONFIG_PPC64
+#define SSP_OFFSET 0x7010
+#else
+#define SSP_OFFSET 0x7008
+#endif
+
+#ifndef __ASSEMBLY__
+
#include <linux/random.h>
#include <linux/version.h>
#include <asm/reg.h>

-extern unsigned long __stack_chk_guard;
-
/*
* Initialize the stackprotector canary value.
*
@@ -34,7 +40,6 @@ static __always_inline void boot_init_stack_canary(void)
canary ^= LINUX_VERSION_CODE;

current->stack_canary = canary;
- __stack_chk_guard = current->stack_canary;
}
-
+#endif /* __ASSEMBLY__ */
#endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 5742dbd..b3a363c 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -34,6 +34,7 @@
#include <asm/ftrace.h>
#include <asm/ptrace.h>
#include <asm/export.h>
+#include <asm/stackprotector.h>

/*
* MSR_KERNEL is > 0x10000 on 4xx/Book-E since it include MSR_CE.
@@ -149,6 +150,9 @@ transfer_to_handler:
mfspr r12,SPRN_SPRG_THREAD
addi r2,r12,-THREAD
tovirt(r2,r2) /* set r2 to current */
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif
beq 2f /* if from user, fix up THREAD.regs */
addi r11,r1,STACK_FRAME_OVERHEAD
stw r11,PT_REGS(r12)
@@ -385,6 +389,9 @@ syscall_exit_cont:
lwz r3,GPR3(r1)
1:
#endif /* CONFIG_TRACE_IRQFLAGS */
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ subi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
/* If the process has its own DBCR0 value, load it up. The internal
debug mode bit tells us that dbcr0 should be loaded. */
@@ -617,6 +624,9 @@ _GLOBAL(_switch)
stwu r1,-INT_FRAME_SIZE(r1)
mflr r0
stw r0,INT_FRAME_SIZE+4(r1)
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ subi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif
/* r3-r12 are caller saved -- Cort */
SAVE_NVGPRS(r1)
stw r0,_NIP(r1) /* Return to switch caller */
@@ -674,10 +684,8 @@ BEGIN_FTR_SECTION
mtspr SPRN_SPEFSCR,r0 /* restore SPEFSCR reg */
END_FTR_SECTION_IFSET(CPU_FTR_SPE)
#endif /* CONFIG_SPE */
-#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
- lwz r0,TSK_STACK_CANARY(r2)
- lis r4,__stack_chk_guard@ha
- stw r0,__stack_chk_guard@l(r4)
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
#endif
lwz r0,_CCR(r1)
mtcrf 0xFF,r0
@@ -779,6 +787,9 @@ user_exc_return: /* r10 contains MSR_KERNEL here */
bne do_work

restore_user:
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ subi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
/* Check whether this process has its own DBCR0 value. The internal
debug mode bit tells us that dbcr0 should be loaded. */
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 9d96354..bae9b83 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -35,6 +35,7 @@
#include <asm/bug.h>
#include <asm/kvm_book3s_asm.h>
#include <asm/export.h>
+#include <asm/stackprotector.h>

/* 601 only have IBAT; cr0.eq is set on 601 when using this macro */
#define LOAD_BAT(n, reg, RA, RB) \
@@ -864,6 +865,9 @@ __secondary_start:
tophys(r4,r2)
addi r4,r4,THREAD /* phys address of our thread_struct */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif
li r3,0
mtspr SPRN_SPRG_RTAS,r3 /* 0 => not in RTAS */

@@ -950,6 +954,9 @@ start_here:
tophys(r4,r2)
addi r4,r4,THREAD /* init task's THREAD */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif
li r3,0
mtspr SPRN_SPRG_RTAS,r3 /* 0 => not in RTAS */

diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index 41374a4..20b1c31 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -42,6 +42,7 @@
#include <asm/asm-offsets.h>
#include <asm/ptrace.h>
#include <asm/export.h>
+#include <asm/stackprotector.h>

/* As with the other PowerPC ports, it is expected that when code
* execution begins here, the following registers contain valid, yet
@@ -835,6 +836,9 @@ start_here:
tophys(r4,r2)
addi r4,r4,THREAD /* init task's THREAD */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif

/* stack */
lis r1,init_thread_union@ha
diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index 37e4a7c..753e2bf 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -40,6 +40,7 @@
#include <asm/ptrace.h>
#include <asm/synch.h>
#include <asm/export.h>
+#include <asm/stackprotector.h>
#include "head_booke.h"

@@ -107,6 +108,9 @@ _ENTRY(_start);
/* ptr to current thread */
addi r4,r2,THREAD /* init task's THREAD */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif

/* stack */
lis r1,init_thread_union@h
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 1a9c99d..49f9ce1 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -32,6 +32,7 @@
#include <asm/ptrace.h>
#include <asm/fixmap.h>
#include <asm/export.h>
+#include <asm/stackprotector.h>

/* Macro to make the code more readable. */
#ifdef CONFIG_8xx_CPU6
@@ -820,6 +821,9 @@ start_here:
tophys(r4,r2)
addi r4,r4,THREAD /* init task's THREAD */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif

/* stack */
lis r1,init_thread_union@ha
diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
index bf4c602..9634ac7 100644
--- a/arch/powerpc/kernel/head_fsl_booke.S
+++ b/arch/powerpc/kernel/head_fsl_booke.S
@@ -43,6 +43,7 @@
#include <asm/cache.h>
#include <asm/ptrace.h>
#include <asm/export.h>
+#include <asm/stackprotector.h>
#include "head_booke.h"

/* As with the other PowerPC ports, it is expected that when code
@@ -235,6 +236,9 @@ set_ivor:
/* ptr to current thread */
addi r4,r2,THREAD /* init task's THREAD */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif

/* stack */
lis r1,init_thread_union@h
@@ -1086,6 +1090,9 @@ __secondary_start:
/* ptr to current thread */
addi r4,r2,THREAD /* address of our thread_struct */
mtspr SPRN_SPRG_THREAD,r4
+#if defined(CONFIG_CC_STACKPROTECTOR)
+ addi r2,r2,TSK_STACK_CANARY+SSP_OFFSET
+#endif

/* Setup the defaults for TLB entries */
li r4,(MAS4_TSIZED(BOOK3E_PAGESZ_4K))@l
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 04885ce..5dd056d 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -64,12 +64,6 @@
#include <linux/kprobes.h>
#include <linux/kdebug.h>

-#ifdef CONFIG_CC_STACKPROTECTOR
-#include <linux/stackprotector.h>
-unsigned long __stack_chk_guard __read_mostly;
-EXPORT_SYMBOL(__stack_chk_guard);
-#endif
-
/* Transactional Memory debug */
#ifdef TM_DEBUG_SW
#define TM_DEBUG(x...) printk(KERN_INFO x)
--
2.10.1

Next message: Shawn Guo: "Re: [PATCH v1 1/3] dt: bindings: add documentation for zx2967 family watchdog controller"
Previous message: Amelie Delaunay: "[PATCH] rtc: stm32: use 0 instead of ~PWR_CR_DBP in regmap_update_bits"
Next in thread: Christian Kujau: "Re: [PATCH RFC] powerpc/32: fix handling of stack protector with recent GCC"
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