From: Vladimir Murzin vladimir.murzin@arm.com
[ Upstream commit 72cd4064fccaae15ab84d40d4be23667402df4ed ]
ARMv8M introduces support for Security extension to M class, among other things it affects exception handling, especially, encoding of EXC_RETURN.
The new bits have been added:
Bit [6] Secure or Non-secure stack Bit [5] Default callee register stacking Bit [0] Exception Secure
which conflicts with hard-coded value of EXC_RETURN:
In fact, we only care of few bits:
Bit [3] Mode (0 - Handler, 1 - Thread) Bit [2] Stack pointer selection (0 - Main, 1 - Process)
We can toggle only those bits and left other bits as they were on exception entry.
It is basically, what patch does - saves EXC_RETURN when we do transition form Thread to Handler mode (it is first svc), so later saved value is used instead of EXC_RET_THREADMODE_PROCESSSTACK.
Signed-off-by: Vladimir Murzin vladimir.murzin@arm.com Signed-off-by: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/include/asm/v7m.h | 2 +- arch/arm/kernel/entry-header.S | 3 ++- arch/arm/kernel/entry-v7m.S | 4 ++++ arch/arm/mm/proc-v7m.S | 3 +++ 4 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/v7m.h b/arch/arm/include/asm/v7m.h index 187ccf6496ad..2cb00d15831b 100644 --- a/arch/arm/include/asm/v7m.h +++ b/arch/arm/include/asm/v7m.h @@ -49,7 +49,7 @@ * (0 -> msp; 1 -> psp). Bits [1:0] are fixed to 0b01. */ #define EXC_RET_STACK_MASK 0x00000004 -#define EXC_RET_THREADMODE_PROCESSSTACK 0xfffffffd +#define EXC_RET_THREADMODE_PROCESSSTACK (3 << 2)
/* Cache related definitions */
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S index 773424843d6e..62db1c9746cb 100644 --- a/arch/arm/kernel/entry-header.S +++ b/arch/arm/kernel/entry-header.S @@ -127,7 +127,8 @@ */ .macro v7m_exception_slow_exit ret_r0 cpsid i - ldr lr, =EXC_RET_THREADMODE_PROCESSSTACK + ldr lr, =exc_ret + ldr lr, [lr]
@ read original r12, sp, lr, pc and xPSR add r12, sp, #S_IP diff --git a/arch/arm/kernel/entry-v7m.S b/arch/arm/kernel/entry-v7m.S index abcf47848525..19d2dcd6530d 100644 --- a/arch/arm/kernel/entry-v7m.S +++ b/arch/arm/kernel/entry-v7m.S @@ -146,3 +146,7 @@ ENTRY(vector_table) .rept CONFIG_CPU_V7M_NUM_IRQ .long __irq_entry @ External Interrupts .endr + .align 2 + .globl exc_ret +exc_ret: + .space 4 diff --git a/arch/arm/mm/proc-v7m.S b/arch/arm/mm/proc-v7m.S index 47a5acc64433..92e84181933a 100644 --- a/arch/arm/mm/proc-v7m.S +++ b/arch/arm/mm/proc-v7m.S @@ -139,6 +139,9 @@ __v7m_setup_cont: cpsie i svc #0 1: cpsid i + ldr r0, =exc_ret + orr lr, lr, #EXC_RET_THREADMODE_PROCESSSTACK + str lr, [r0] ldmia sp, {r0-r3, r12} str r5, [r12, #11 * 4] @ restore the original SVC vector entry mov lr, r6 @ restore LR