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authorRussell King <rmk+kernel@armlinux.org.uk>2017-11-24 23:49:34 +0000
committerRussell King <rmk+kernel@armlinux.org.uk>2017-11-26 15:41:39 +0000
commit8bafae202c82dc257f649ea3c275a0f35ee15113 (patch)
tree1c2a7d64f216df552e4509dc746d8da3436e39ab
parent400eeffaffc7232c0ae1134fe04e14ae4fb48d8c (diff)
ARM: BUG if jumping to usermode address in kernel mode
Detect if we are returning to usermode via the normal kernel exit paths but the saved PSR value indicates that we are in kernel mode. This could occur due to corrupted stack state, which has been observed with "ftracetest". This ensures that we catch the problem case before we get to user code. Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
-rw-r--r--arch/arm/include/asm/assembler.h18
-rw-r--r--arch/arm/kernel/entry-header.S6
2 files changed, 24 insertions, 0 deletions
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index ad301f107dd2..bc8d4bbd82e2 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -518,4 +518,22 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
#endif
.endm
+ .macro bug, msg, line
+#ifdef CONFIG_THUMB2_KERNEL
+1: .inst 0xde02
+#else
+1: .inst 0xe7f001f2
+#endif
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+ .pushsection .rodata.str, "aMS", %progbits, 1
+2: .asciz "\msg"
+ .popsection
+ .pushsection __bug_table, "aw"
+ .align 2
+ .word 1b, 2b
+ .hword \line
+ .popsection
+#endif
+ .endm
+
#endif /* __ASM_ASSEMBLER_H__ */
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 6391728c8f03..75f7a4e8541a 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -299,6 +299,8 @@
mov r2, sp
ldr r1, [r2, #\offset + S_PSR] @ get calling cpsr
ldr lr, [r2, #\offset + S_PC]! @ get pc
+ tst r1, #0xcf
+ bne 1f
msr spsr_cxsf, r1 @ save in spsr_svc
#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
@ We must avoid clrex due to Cortex-A15 erratum #830321
@@ -313,6 +315,7 @@
@ after ldm {}^
add sp, sp, #\offset + PT_REGS_SIZE
movs pc, lr @ return & move spsr_svc into cpsr
+1: bug "Returning to usermode but unexpected PSR bits set?", \@
#elif defined(CONFIG_CPU_V7M)
@ V7M restore.
@ Note that we don't need to do clrex here as clearing the local
@@ -328,6 +331,8 @@
ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
ldr lr, [sp, #\offset + S_PC] @ get pc
add sp, sp, #\offset + S_SP
+ tst r1, #0xcf
+ bne 1f
msr spsr_cxsf, r1 @ save in spsr_svc
@ We must avoid clrex due to Cortex-A15 erratum #830321
@@ -340,6 +345,7 @@
.endif
add sp, sp, #PT_REGS_SIZE - S_SP
movs pc, lr @ return & move spsr_svc into cpsr
+1: bug "Returning to usermode but unexpected PSR bits set?", \@
#endif /* !CONFIG_THUMB2_KERNEL */
.endm