linux-kernel - [PATCH 4.9 058/148] ARM: avoid faulting on qemu

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Date:   Tue, 12 Dec 2017 13:44:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Russell King <rmk+kernel@...linux.org.uk>,
        Alex Shi <alex.shi@...aro.org>
Subject: [PATCH 4.9 058/148] ARM: avoid faulting on qemu

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Russell King <rmk+kernel@...linux.org.uk>

commit 3aaf33bebda8d4ffcc0fc8ef39e6c1ac68823b11 upstream.

When qemu starts a kernel in a bare environment, the default SCR has
the AW and FW bits clear, which means that the kernel can't modify
the PSR A or PSR F bits, and means that FIQs and imprecise aborts are
always masked.

When running uboot under qemu, the AW and FW SCR bits are set, and the
kernel functions normally - and this is how real hardware behaves.

Fix this for qemu by ignoring the FIQ bit.

Fixes: 8bafae202c82 ("ARM: BUG if jumping to usermode address in kernel mode")
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
Cc: Alex Shi <alex.shi@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm/kernel/entry-header.S |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -299,7 +299,7 @@
 	mov	r2, sp
 	ldr	r1, [r2, #\offset + S_PSR]	@ get calling cpsr
 	ldr	lr, [r2, #\offset + S_PC]!	@ get pc
-	tst	r1, #0xcf
+	tst	r1, #PSR_I_BIT | 0x0f
 	bne	1f
 	msr	spsr_cxsf, r1			@ save in spsr_svc
 #if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
@@ -331,7 +331,7 @@
 	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
+	tst	r1, #PSR_I_BIT | 0x0f
 	bne	1f
 	msr	spsr_cxsf, r1			@ save in spsr_svc