linux-kernel - [PATCH 1/9] signal/sh: Use force_sig(SIGKILL) instead of do_group

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Date:   Thu, 24 Jun 2021 13:59:04 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Michael Schmitz <schmitzmic@...il.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Tejun Heo <tj@...nel.org>, Kees Cook <keescook@...omium.org>
Subject: [PATCH 1/9] signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL)


Today the sh code allocates memory the first time a process uses
the fpu.  If that memory allocation fails kill the affected task
with force_sig(SIGKILL) rather than do_group_exit(SIGKILL).

Calling do_group_exit from an exception handler can potentially lead
to locking dead locks as do_group_exit is not designed to be called
from interrupt context.  Instead use force_sig(SIGKILL) to kill
the userspace process.  Sending signals in general and force_sig
in particular has been tested from interrupt context so there
should be no problems.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 arch/sh/kernel/cpu/fpu.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/sh/kernel/cpu/fpu.c b/arch/sh/kernel/cpu/fpu.c
index ae354a2931e7..fd6db0ab1928 100644
--- a/arch/sh/kernel/cpu/fpu.c
+++ b/arch/sh/kernel/cpu/fpu.c
@@ -62,18 +62,20 @@ void fpu_state_restore(struct pt_regs *regs)
 	}
 
 	if (!tsk_used_math(tsk)) {
-		local_irq_enable();
+		int ret;
 		/*
 		 * does a slab alloc which can sleep
 		 */
-		if (init_fpu(tsk)) {
+		local_irq_enable();
+		ret = init_fpu(tsk);
+		local_irq_disable();
+		if (ret) {
 			/*
 			 * ran out of memory!
 			 */
-			do_group_exit(SIGKILL);
+			force_sig(SIGKILL);
 			return;
 		}
-		local_irq_disable();
 	}
 
 	grab_fpu(regs);
-- 
2.20.1