[PATCH 1/3] x86/mce: Change to not send SIGBUS error during copy from user

Tony Luck
2021-07-06T19:06:29Z

Sending a SIGBUS for a copy from user is not the correct semantic.
System calls should return -EFAULT (or a short count for write(2)).

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
arch/x86/kernel/cpu/mce/core.c | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 22791aadc085..dd03971e5ad5 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1265,7 +1265,7 @@ static void kill_me_maybe(struct callback_head *cb)
flags |= MF_MUST_KILL;

ret = memory_failure(p->mce_addr >> PAGE_SHIFT, flags);
- if (!ret && !(p->mce_kflags & MCE_IN_KERNEL_COPYIN)) {
+ if (!ret) {
set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
sync_core();
return;
@@ -1279,25 +1279,27 @@ static void kill_me_maybe(struct callback_head *cb)
if (ret == -EHWPOISON)
return;

- if (p->mce_vaddr != (void __user *)-1l) {
- force_sig_mceerr(BUS_MCEERR_AR, p->mce_vaddr, PAGE_SHIFT);
- } else {
- pr_err("Memory error not recovered");
- kill_me_now(cb);
- }
+ pr_err("Memory error not recovered");
+ kill_me_now(cb);
+}
+
+static void kill_me_never(struct callback_head *cb)
+{
+ struct task_struct *p = container_of(cb, struct task_struct, mce_kill_me);
+
+ pr_err("Kernel accessed poison in user space at %llx\n", p->mce_addr);
+ if (!memory_failure(p->mce_addr >> PAGE_SHIFT, 0))
+ set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
}

-static void queue_task_work(struct mce *m, int kill_current_task)
+static void queue_task_work(struct mce *m, void (*func)(struct callback_head *))
{
current->mce_addr = m->addr;
current->mce_kflags = m->kflags;
current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV);
current->mce_whole_page = whole_page(m);

- if (kill_current_task)
- current->mce_kill_me.func = kill_me_now;
- else
- current->mce_kill_me.func = kill_me_maybe;
+ current->mce_kill_me.func = func;

task_work_add(current, &current->mce_kill_me, TWA_RESUME);
}
@@ -1435,7 +1437,10 @@ noinstr void do_machine_check(struct pt_regs *regs)
/* If this triggers there is no way to recover. Die hard. */
BUG_ON(!on_thread_stack() || !user_mode(regs));

- queue_task_work(&m, kill_current_task);
+ if (kill_current_task)
+ queue_task_work(&m, kill_me_now);
+ else
+ queue_task_work(&m, kill_me_maybe);

} else {
/*
@@ -1453,7 +1458,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
}

if (m.kflags & MCE_IN_KERNEL_COPYIN)
- queue_task_work(&m, kill_current_task);
+ queue_task_work(&m, kill_me_never);
}
out:
mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
--
2.29.2