From: Will Deacon <will.deacon@xxxxxxx>
When running a compat (AArch32) userspace on Cortex-A53, a load at EL0
from a virtual address that matches the bottom 32 bits of the virtual
address used by a recent load at (AArch64) EL1 might return incorrect
data.
This patch works around the issue by writing to the contextidr_el1
register on the exception return path when returning to a 32-bit task.
This workaround is patched in at runtime based on the MIDR value of the
processor.
Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Tested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 3.19+
(cherry picked from commit 905e8c5dcaa147163672b06fe9dcb5abaacbc711)
Signed-off-by: Kevin Hilman <khilman@xxxxxxxxxx>
---
arch/arm64/Kconfig | 21 +++++++++++++++++++++
arch/arm64/include/asm/cpufeature.h | 3 ++-
arch/arm64/kernel/cpu_errata.c | 8 ++++++++
arch/arm64/kernel/entry.S | 20 ++++++++++++++++++++
4 files changed, 51 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b1f9a20a3677..77fb593b3f4c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -306,6 +306,27 @@ config ARM64_ERRATUM_832075
If unsure, say Y.
+config ARM64_ERRATUM_845719
+ bool "Cortex-A53: 845719: a load might read incorrect data"
+ depends on COMPAT
+ default y
+ help
+ This option adds an alternative code sequence to work around ARM
+ erratum 845719 on Cortex-A53 parts up to r0p4.
+
+ When running a compat (AArch32) userspace on an affected Cortex-A53
+ part, a load at EL0 from a virtual address that matches the bottom 32
+ bits of the virtual address used by a recent load at (AArch64) EL1
+ might return incorrect data.
+
+ The workaround is to write the contextidr_el1 register on exception
+ return to a 32-bit task.
+ Please note that this does not necessarily enable the workaround,
+ as it depends on the alternative framework, which will only patch
+ the kernel if an affected CPU is detected.
+
+ If unsure, say Y.
+
endmenu
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 07547ccc1f2b..5fe4befda1a5 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -23,8 +23,9 @@
#define ARM64_WORKAROUND_CLEAN_CACHE 0
#define ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE 1
+#define ARM64_WORKAROUND_845719 2
-#define ARM64_NCAPS 2
+#define ARM64_NCAPS 3
#ifndef __ASSEMBLY__
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 7c4849489515..ad6d52392bb1 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -92,6 +92,14 @@ struct arm64_cpu_capabilities arm64_errata[] = {
(1 << MIDR_VARIANT_SHIFT) | 2),
},
#endif
+#ifdef CONFIG_ARM64_ERRATUM_845719
+ {
+ /* Cortex-A53 r0p[01234] */
+ .desc = "ARM erratum 845719",
+ .capability = ARM64_WORKAROUND_845719,
+ MIDR_RANGE(MIDR_CORTEX_A53, 0x00, 0x04),
+ },
+#endif
{
}
};
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index fd4fa374e5d2..9b870a2815e6 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -21,8 +21,10 @@
#include <linux/init.h>
#include <linux/linkage.h>
+#include <asm/alternative-asm.h>
#include <asm/assembler.h>
#include <asm/asm-offsets.h>
+#include <asm/cpufeature.h>
#include <asm/errno.h>
#include <asm/esr.h>
#include <asm/thread_info.h>
@@ -120,6 +122,24 @@
ct_user_enter
ldr x23, [sp, #S_SP] // load return stack pointer
msr sp_el0, x23
+
+#ifdef CONFIG_ARM64_ERRATUM_845719
+ alternative_insn \
+ "nop", \
+ "tbz x22, #4, 1f", \
+ ARM64_WORKAROUND_845719
+#ifdef CONFIG_PID_IN_CONTEXTIDR
+ alternative_insn \
+ "nop; nop", \
+ "mrs x29, contextidr_el1; msr contextidr_el1, x29; 1:", \
+ ARM64_WORKAROUND_845719
+#else
+ alternative_insn \
+ "nop", \
+ "msr contextidr_el1, xzr; 1:", \
+ ARM64_WORKAROUND_845719
+#endif
+#endif
.endif
msr elr_el1, x21 // set up the return data
msr spsr_el1, x22
--
2.3.1
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