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BACKPORT: FROMLIST: 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.

Signed-off-by: Will Deacon <will@kernel.org>
Bug: 178507149
Link: https://lore.kernel.org/linux-arch/20201208132835.6151-5-will@kernel.org/
[will: Fixed trivial conflict with vendor hook in __switch_to()]
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I5ae90f3fb63499d7016f93d13e32693e26890f92
This commit is contained in:
Will Deacon
2020-10-27 21:00:02 +00:00
committed by Will Deacon
parent a0888cb3a9
commit c7d6ec319b
2 changed files with 44 additions and 1 deletions
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19
arch/arm64/kernel/process.c
View File

@@ -538,6 +538,15 @@ 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);
}
/*
* Thread switching.
*/
@@ -554,6 +563,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
uao_thread_switch(next);
ssbs_thread_switch(next);
erratum_1418040_thread_switch(prev, next);
compat_thread_switch(next);
/*
* vendor hook is needed before the dsb(),
* because MPAM is related to cache maintenance.
@@ -623,8 +633,15 @@ 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(current);
if (task_spec_ssb_noexec(current)) {

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)
{
@@ -941,6 +954,19 @@ 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)