From: Rabin Vincent <rabin@rab.in>
To: jesper.nilsson@axis.com
Cc: linux-cris-kernel@axis.com, viro@zeniv.linux.org.uk,
linux-kernel@vger.kernel.org, Rabin Vincent <rabin@rab.in>
Subject: [PATCH 1/3] CRISv32: don't attempt syscall restart on irq exit
Date: Sun, 8 Feb 2015 21:45:02 +0100 [thread overview]
Message-ID: <1423428304-26586-1-git-send-email-rabin@rab.in> (raw)
r9 is used to determine whether syscall restarting must be performed or
not. Unfortunately, r9 is never set to zero in the non-syscall path,
and r9 is on top of that a callee-saved register which can be set to
non-zero by the C functions that are called during IRQ handling.
This means that if r10 (used for the syscall return value) is one of the
-ERESTART* values when a hardware interrupt occurs which leads to a
signal being delivered to the process, the kernel will "restart" a
syscall which never occurred. This will lead to the PC being moved back
by 2 on return to user space.
Fix the problem by setting r9 to zero in the interrupt path.
Test case (should loop forever but ends up executing the break 8 trap
instruction):
#include <signal.h>
#include <stdlib.h>
#include <sys/time.h>
void f(int n)
{
register int r9 asm ("r9") = 1;
register int r10 asm ("r10") = n;
__asm__ __volatile__(
"ba 1f \n"
"nop \n"
"break 8 \n"
"1: ba . \n"
"nop \n"
:
: "r" (r9), "r" (r10)
: "memory");
}
void handler1(int sig) { }
int main(int argc, char *argv[])
{
struct itimerval t1 = { .it_value = {1} };
signal(SIGALRM, handler1);
setitimer(ITIMER_REAL, &t1, NULL);
f(-513); /* -ERESTARTNOINTR */
return 0;
}
Signed-off-by: Rabin Vincent <rabin@rab.in>
---
arch/cris/arch-v32/kernel/entry.S | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/cris/arch-v32/kernel/entry.S b/arch/cris/arch-v32/kernel/entry.S
index 2f19ac6..d4c088b 100644
--- a/arch/cris/arch-v32/kernel/entry.S
+++ b/arch/cris/arch-v32/kernel/entry.S
@@ -99,6 +99,8 @@ ret_from_kernel_thread:
.type ret_from_intr,@function
ret_from_intr:
+ moveq 0, $r9 ; not a syscall
+
;; Check for resched if preemptive kernel, or if we're going back to
;; user-mode. This test matches the user_regs(regs) macro. Don't simply
;; test CCS since that doesn't necessarily reflect what mode we'll
--
2.1.4
next reply other threads:[~2015-02-08 20:45 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-08 20:45 Rabin Vincent [this message]
2015-02-08 20:45 ` [PATCH 2/3] CRISv32: prevent bogus restarts on sigreturn Rabin Vincent
2015-02-09 9:51 ` Jesper Nilsson
2015-02-08 20:45 ` [PATCH 3/3] CRISv32: handle multiple signals Rabin Vincent
2015-02-09 2:03 ` Guenter Roeck
2015-02-09 9:57 ` Jesper Nilsson
2015-02-09 14:16 ` Guenter Roeck
2015-02-09 16:57 ` Guenter Roeck
2015-02-10 8:21 ` Jesper Nilsson
[not found] ` <CAJy5ezog4wmV13muOsVopwYhV7QYE6kwqFtJx0rsh+5Z4bf1tg@mail.gmail.com>
2015-02-10 12:26 ` Guenter Roeck
2015-02-09 9:52 ` Jesper Nilsson
2015-02-09 9:49 ` [PATCH 1/3] CRISv32: don't attempt syscall restart on irq exit Jesper Nilsson
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