From: ebiederm@xmission.com (Eric W. Biederman)
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: kstewart@linuxfoundation.org, gustavo@embeddedor.com,
gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
Jing Xiangfeng <jingxiangfeng@huawei.com>,
linux-mm@kvack.org, sakari.ailus@linux.intel.com,
bhelgaas@google.com, tglx@linutronix.de,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm: fix page faults in do_alignment
Date: Fri, 30 Aug 2019 14:45:36 -0500 [thread overview]
Message-ID: <87d0gmwi73.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20190830133522.GZ13294@shell.armlinux.org.uk> (Russell King's message of "Fri, 30 Aug 2019 14:35:22 +0100")
Russell King - ARM Linux admin <linux@armlinux.org.uk> writes:
> On Fri, Aug 30, 2019 at 09:31:17PM +0800, Jing Xiangfeng wrote:
>> The function do_alignment can handle misaligned address for user and
>> kernel space. If it is a userspace access, do_alignment may fail on
>> a low-memory situation, because page faults are disabled in
>> probe_kernel_address.
>>
>> Fix this by using __copy_from_user stead of probe_kernel_address.
>>
>> Fixes: b255188 ("ARM: fix scheduling while atomic warning in alignment handling code")
>> Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
>
> NAK.
>
> The "scheduling while atomic warning in alignment handling code" is
> caused by fixing up the page fault while trying to handle the
> mis-alignment fault generated from an instruction in atomic context.
>
> Your patch re-introduces that bug.
And the patch that fixed scheduling while atomic apparently introduced a
regression. Admittedly a regression that took 6 years to track down but
still.
So it looks like the code needs to do something like:
diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index 04b36436cbc0..5e2b8623851e 100644
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -784,6 +784,9 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
instrptr = instruction_pointer(regs);
+ if (user_mode(regs))
+ goto user;
+
if (thumb_mode(regs)) {
u16 *ptr = (u16 *)(instrptr & ~1);
fault = probe_kernel_address(ptr, tinstr);
@@ -933,6 +936,34 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
return 1;
user:
+ if (thumb_mode(regs)) {
+ u16 *ptr = (u16 *)(instrptr & ~1);
+ fault = get_user(tinstr, ptr);
+ tinstr = __mem_to_opcode_thumb16(tinstr);
+ if (!fault) {
+ if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
+ IS_T32(tinstr)) {
+ /* Thumb-2 32-bit */
+ u16 tinst2 = 0;
+ fault = get_user(ptr + 1, tinst2);
+ tinst2 = __mem_to_opcode_thumb16(tinst2);
+ instr = __opcode_thumb32_compose(tinstr, tinst2);
+ thumb2_32b = 1;
+ } else {
+ isize = 2;
+ instr = thumb2arm(tinstr);
+ }
+ }
+ } else {
+ fault = get_user(instr, (u32*)instrptr);
+ instr = __mem_to_opcode_arm(instr);
+ }
+
+ if (fault) {
+ type = TYPE_FAULT;
+ goto bad_or_fault;
+ }
+
ai_user += 1;
if (ai_usermode & UM_WARN)
Eric
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next prev parent reply other threads:[~2019-08-30 19:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 13:31 [PATCH] arm: fix page faults in do_alignment Jing Xiangfeng
2019-08-30 13:35 ` Russell King - ARM Linux admin
2019-08-30 13:48 ` Russell King - ARM Linux admin
2019-08-30 19:45 ` Eric W. Biederman [this message]
2019-08-30 20:30 ` Russell King - ARM Linux admin
2019-08-30 21:02 ` Eric W. Biederman
2019-08-30 22:29 ` Russell King - ARM Linux admin
2019-09-02 17:36 ` Eric W. Biederman
2019-09-04 2:17 ` Jing Xiangfeng
2019-09-06 15:17 ` Russell King - ARM Linux admin
2019-09-15 18:34 ` Russell King - ARM Linux admin
2019-09-16 14:31 ` Eric W. Biederman
2019-08-31 1:49 ` Jing Xiangfeng
2019-08-31 7:55 ` Russell King - ARM Linux admin
2019-08-31 9:16 ` Jing Xiangfeng
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