From: D Scott Phillips <scott@xxxxxxxxxxxxxxxxxxxxxx>
commit 38e0257e0e6f4fef2aa2966b089b56a8b1cfb75c upstream.
The erratum 1418040 workaround enables CNTVCT_EL1 access trapping in EL0
when executing compat threads. The workaround is applied when switching
between tasks, but the need for the workaround could also change at an
exec(), when a non-compat task execs a compat binary or vice versa. Apply
the workaround in arch_setup_new_exec().
This leaves a small window of time between SET_PERSONALITY and
arch_setup_new_exec where preemption could occur and confuse the old
workaround logic that compares TIF_32BIT between prev and next. Instead, we
can just read cntkctl to make sure it's in the state that the next task
needs. I measured cntkctl read time to be about the same as a mov from a
general-purpose register on N1. Update the workaround logic to examine the
current value of cntkctl instead of the previous task's compat state.
Fixes: d49f7d7376d0 ("arm64: Move handling of erratum 1418040 into C code")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.9.x
Signed-off-by: D Scott Phillips <scott@xxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20211220234114.3926-1-scott@xxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
arch/arm64/kernel/process.c | 39 +++++++++++++++----------------------
1 file changed, 16 insertions(+), 23 deletions(-)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f7c42a7d09b6..c108d96a22db 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -515,34 +515,26 @@ static void entry_task_switch(struct task_struct *next)
/*
* ARM erratum 1418040 handling, affecting the 32bit view of CNTVCT.
- * Assuming the virtual counter is enabled at the beginning of times:
- *
- * - disable access when switching from a 64bit task to a 32bit task
- * - enable access when switching from a 32bit task to a 64bit task
+ * Ensure access is disabled when switching to a 32bit task, ensure
+ * access is enabled when switching to a 64bit task.
*/
-static void erratum_1418040_thread_switch(struct task_struct *prev,
- struct task_struct *next)
+static void erratum_1418040_thread_switch(struct task_struct *next)
{
- bool prev32, next32;
- u64 val;
-
- if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040))
- return;
-
- prev32 = is_compat_thread(task_thread_info(prev));
- next32 = is_compat_thread(task_thread_info(next));
-
- if (prev32 == next32 || !this_cpu_has_cap(ARM64_WORKAROUND_1418040))
+ if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) ||
+ !this_cpu_has_cap(ARM64_WORKAROUND_1418040))
return;
- val = read_sysreg(cntkctl_el1);
-
- if (!next32)
- val |= ARCH_TIMER_USR_VCT_ACCESS_EN;
+ if (is_compat_thread(task_thread_info(next)))
+ sysreg_clear_set(cntkctl_el1, ARCH_TIMER_USR_VCT_ACCESS_EN, 0);
else
- val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN;
+ sysreg_clear_set(cntkctl_el1, 0, ARCH_TIMER_USR_VCT_ACCESS_EN);
+}
- write_sysreg(val, cntkctl_el1);
+static void erratum_1418040_new_exec(void)
+{
+ preempt_disable();
+ erratum_1418040_thread_switch(current);
+ preempt_enable();
}
/*
@@ -560,7 +552,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
entry_task_switch(next);
uao_thread_switch(next);
ssbs_thread_switch(next);
- erratum_1418040_thread_switch(prev, next);
+ erratum_1418040_thread_switch(next);
/*
* Complete any pending TLB or cache maintenance on this CPU in case
@@ -619,6 +611,7 @@ void arch_setup_new_exec(void)
current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
ptrauth_thread_init_user(current);
+ erratum_1418040_new_exec();
}
#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
