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arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs

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Scheduling a 32-bit application on a 64-bit-only CPU is a bad idea.

Ensure that 32-bit applications always take the slow-path when returning
to userspace on a system with mismatched support at EL0, so that we can
avoid trying to run on a 64-bit-only CPU and force a SIGKILL instead.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210608180313.11502-5-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon 2021-06-08 19:02:57 +01:00
parent 2f6a49bbc0
commit 873c3e8977
2 changed files with 44 additions and 1 deletions
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19
arch/arm64/kernel/process.c
View File

@ -527,6 +527,15 @@ static void erratum_1418040_thread_switch(struct task_struct *prev,
write_sysreg(val, cntkctl_el1);
}
static void compat_thread_switch(struct task_struct *next)
{
if (!is_compat_thread(task_thread_info(next)))
return;
if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
set_tsk_thread_flag(next, TIF_NOTIFY_RESUME);
}
static void update_sctlr_el1(u64 sctlr)
{
/*
@ -568,6 +577,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
ssbs_thread_switch(next);
erratum_1418040_thread_switch(prev, next);
ptrauth_thread_switch_user(next);
compat_thread_switch(next);
/*
* Complete any pending TLB or cache maintenance on this CPU in case
@ -633,8 +643,15 @@ unsigned long arch_align_stack(unsigned long sp)
*/
void arch_setup_new_exec(void)
{
current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
unsigned long mmflags = 0;
if (is_compat_task()) {
mmflags = MMCF_AARCH32;
if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
}
current->mm->context.flags = mmflags;
ptrauth_thread_init_user();
mte_thread_init_user();

26
arch/arm64/kernel/signal.c
View File

@ -911,6 +911,19 @@ static void do_signal(struct pt_regs *regs)
restore_saved_sigmask();
}
static bool cpu_affinity_invalid(struct pt_regs *regs)
{
if (!compat_user_mode(regs))
return false;
/*
* We're preemptible, but a reschedule will cause us to check the
* affinity again.
*/
return !cpumask_test_cpu(raw_smp_processor_id(),
system_32bit_el0_cpumask());
}
asmlinkage void do_notify_resume(struct pt_regs *regs,
unsigned long thread_flags)
{
@ -938,6 +951,19 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
if (thread_flags & _TIF_NOTIFY_RESUME) {
tracehook_notify_resume(regs);
rseq_handle_notify_resume(NULL, regs);
/*
* If we reschedule after checking the affinity
* then we must ensure that TIF_NOTIFY_RESUME
* is set so that we check the affinity again.
* Since tracehook_notify_resume() clears the
* flag, ensure that the compiler doesn't move
* it after the affinity check.
*/
barrier();
if (cpu_affinity_invalid(regs))
force_sig(SIGKILL);
}
if (thread_flags & _TIF_FOREIGN_FPSTATE)