linux-kernel - Re: [PATCH 2/2] riscv: misaligned: fix sleeping function called during misaligned access handling

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Message-ID: <CAHh=Yk-jk-KzDK_kJTbGi8HOZqsUPZjdGN8eF_op=HKF2V-Udw@mail.gmail.com>
Date: Tue, 29 Apr 2025 13:57:35 +0800
From: Nylon Chen <nylon.chen@...ive.com>
To: Clément Léger <cleger@...osinc.com>
Cc: Alexandre Ghiti <alex@...ti.fr>, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu, charlie@...osinc.com, jesse@...osinc.com, 
	evan@...osinc.com, zhangchunyan@...as.ac.cn, samuel.holland@...ive.com, 
	zong.li@...ive.com
Subject: Re: [PATCH 2/2] riscv: misaligned: fix sleeping function called
 during misaligned access handling

Hi Clément,

Thank you for sharing your patch. I’ve reviewed the changes, but I’m
not sure I fully grasp the design rationale.
Could you please briefly explain the main considerations behind this
modification?

We’re also discussing internally the differences between my _nofault
approach and your IRQ-enable approach, and I’d appreciate your
perspective on the pros and cons of each.

Looking forward to your suggestions!

Nylon

Clément Léger <cleger@...osinc.com> 於 2025年4月11日 週五 下午4:38寫道：
>
>
>
> On 11/04/2025 10:35, Alexandre Ghiti wrote:
> > Hi Clément,
> >
> > On 11/04/2025 09:36, Clément Léger wrote:
> >> Hi Nylon,
> >>
> >> I already have a pending fix for that bug which is to reenable
> >> interrupts while handling misaligned faults. Please see:
> >> https://lore.kernel.org/linux-riscv/20250317170625.1142870-12-
> >> cleger@...osinc.com/
> >
> >
> > Can you extract this fix from the series so that it can be merged in 6.15?
>
> Hi Alex,
>
> Yes sure, I can send a small series as well. However, I'd like the
> associated kselftest to be reviewed since it would allow to catch such
> behavior (there is no test for misaligned delegation yet).
>
> Thanks,
>
> Clément
>
> >
> > Thanks,
> >
> > Alex
> >
> >
> >>
> >> Thanks,
> >>
> >> Clément
> >>
> >> On 11/04/2025 09:38, Nylon Chen wrote:
> >>> Use copy_from_user_nofault() and copy_to_user_nofault() instead of
> >>> copy_from/to_user functions in the misaligned access trap handlers.
> >>>
> >>> The following bug report was found when executing misaligned memory
> >>> accesses:
> >>>
> >>> BUG: sleeping function called from invalid context at ./include/
> >>> linux/uaccess.h:162
> >>> in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 115, name: two
> >>> preempt_count: 0, expected: 0
> >>> CPU: 0 UID: 0 PID: 115 Comm: two Not tainted 6.14.0-rc5 #24
> >>> Hardware name: riscv-virtio,qemu (DT)
> >>> Call Trace:
> >>>   [<ffffffff800160ea>] dump_backtrace+0x1c/0x24
> >>>   [<ffffffff80002304>] show_stack+0x28/0x34
> >>>   [<ffffffff80010fae>] dump_stack_lvl+0x4a/0x68
> >>>   [<ffffffff80010fe0>] dump_stack+0x14/0x1c
> >>>   [<ffffffff8004e44e>] __might_resched+0xfa/0x104
> >>>   [<ffffffff8004e496>] __might_sleep+0x3e/0x62
> >>>   [<ffffffff801963c4>] __might_fault+0x1c/0x24
> >>>   [<ffffffff80425352>] _copy_from_user+0x28/0xaa
> >>>   [<ffffffff8000296c>] handle_misaligned_store+0x204/0x254
> >>>   [<ffffffff809eae82>] do_trap_store_misaligned+0x24/0xee
> >>>   [<ffffffff809f4f1a>] handle_exception+0x146/0x152
> >>>
> >>> Fixes: b686ecdeacf6 ("riscv: misaligned: Restrict user access to
> >>> kernel memory")
> >>> Fixes: 441381506ba7 ("riscv: misaligned: remove CONFIG_RISCV_M_MODE
> >>> specific code")
> >>>
> >>> Signed-off-by: Zong Li <zong.li@...ive.com>
> >>> Signed-off-by: Nylon Chen <nylon.chen@...ive.com>
> >>> ---
> >>>   arch/riscv/kernel/traps_misaligned.c | 4 ++--
> >>>   1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/
> >>> kernel/traps_misaligned.c
> >>> index d7275dfb6b7e..563f73f88fa8 100644
> >>> --- a/arch/riscv/kernel/traps_misaligned.c
> >>> +++ b/arch/riscv/kernel/traps_misaligned.c
> >>> @@ -455,7 +455,7 @@ static int handle_scalar_misaligned_load(struct
> >>> pt_regs *regs)
> >>>         val.data_u64 = 0;
> >>>       if (user_mode(regs)) {
> >>> -        if (copy_from_user(&val, (u8 __user *)addr, len))
> >>> +        if (copy_from_user_nofault(&val, (u8 __user *)addr, len))
> >>>               return -1;
> >>>       } else {
> >>>           memcpy(&val, (u8 *)addr, len);
> >>> @@ -556,7 +556,7 @@ static int handle_scalar_misaligned_store(struct
> >>> pt_regs *regs)
> >>>           return -EOPNOTSUPP;
> >>>         if (user_mode(regs)) {
> >>> -        if (copy_to_user((u8 __user *)addr, &val, len))
> >>> +        if (copy_to_user_nofault((u8 __user *)addr, &val, len))
> >>>               return -1;
> >>>       } else {
> >>>           memcpy((u8 *)addr, &val, len);
> >>
> >> _______________________________________________
> >> linux-riscv mailing list
> >> linux-riscv@...ts.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
>

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