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Subject[tip: ras/core] x86/mce: Change to not send SIGBUS error during copy from user
The following commit has been merged into the ras/core branch of tip:

Commit-ID: a6e3cf70b772541c2388abdb86e5a562cfe18e63
Gitweb: https://git.kernel.org/tip/a6e3cf70b772541c2388abdb86e5a562cfe18e63
Author: Tony Luck <tony.luck@intel.com>
AuthorDate: Tue, 17 Aug 2021 17:29:41 -07:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 20 Sep 2021 10:55:41 +02:00

x86/mce: Change to not send SIGBUS error during copy from user

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>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210818002942.1607544-3-tony.luck@intel.com
---
arch/x86/kernel/cpu/mce/core.c | 35 ++++++++++++++++++---------------
1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 193204a..69768fe 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1272,7 +1272,7 @@ 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;
@@ -1286,15 +1286,21 @@ 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);
+
+ p->mce_count = 0;
+ 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, char *msg, int kill_current_task)
+static void queue_task_work(struct mce *m, char *msg, void (*func)(struct callback_head *))
{
int count = ++current->mce_count;

@@ -1304,11 +1310,7 @@ static void queue_task_work(struct mce *m, char *msg, int kill_current_task)
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;
}

/* Ten is likely overkill. Don't expect more than two faults before task_work() */
@@ -1459,7 +1461,10 @@ 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, msg, kill_current_task);
+ if (kill_current_task)
+ queue_task_work(&m, msg, kill_me_now);
+ else
+ queue_task_work(&m, msg, kill_me_maybe);

} else {
/*
@@ -1477,7 +1482,7 @@ noinstr void do_machine_check(struct pt_regs *regs)
}

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