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Subject[PATCH v2 02/18] arm64: Add CNTVCT_EL0 trap handler
Date
Since people seem to make a point in breaking the userspace visible
counter, we have no choice but to trap the access. Add the required
handler.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/include/asm/esr.h | 2 ++
arch/arm64/kernel/traps.c | 14 ++++++++++++++
2 files changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index d14c478976d0..ad42e79a5d4d 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -175,6 +175,8 @@
#define ESR_ELx_SYS64_ISS_SYS_CTR_READ (ESR_ELx_SYS64_ISS_SYS_CTR | \
ESR_ELx_SYS64_ISS_DIR_READ)

+#define ESR_ELx_SYS64_ISS_SYS_CNTVCT (ESR_ELx_SYS64_ISS_SYS_VAL(3, 3, 2, 14, 0) | \
+ ESR_ELx_SYS64_ISS_DIR_READ)
#ifndef __ASSEMBLY__
#include <asm/types.h>

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index e52be6aa44ee..1de444e6c669 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -505,6 +505,14 @@ static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
regs->pc += 4;
}

+static void cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
+{
+ int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+
+ pt_regs_write_reg(regs, rt, arch_counter_get_cntvct());
+ regs->pc += 4;
+}
+
struct sys64_hook {
unsigned int esr_mask;
unsigned int esr_val;
@@ -523,6 +531,12 @@ static struct sys64_hook sys64_hooks[] = {
.esr_val = ESR_ELx_SYS64_ISS_SYS_CTR_READ,
.handler = ctr_read_handler,
},
+ {
+ /* Trap read access to CNTVCT_EL0 */
+ .esr_mask = ESR_ELx_SYS64_ISS_SYS_OP_MASK,
+ .esr_val = ESR_ELx_SYS64_ISS_SYS_CNTVCT,
+ .handler = cntvct_read_handler,
+ },
{},
};

--
2.11.0
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