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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Mon, 10 Oct 2022 13:06:19 +0200
Message-ID: <CAMj1kXHn70rRaB=BgCrMoqQxRcq=HzZ0NWFYL+FqV_037PaY3w@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] ARM: Fix some check warnings of tool sparse
To:     "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Cc:     Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
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On Mon, 10 Oct 2022 at 12:58, Leizhen (ThunderTown)
<thunder.leizhen@huawei.com> wrote:
>
>
>
> On 2022/10/10 18:20, Ard Biesheuvel wrote:
> > On Mon, 10 Oct 2022 at 11:56, Zhen Lei <thunder.leizhen@huawei.com> wrote:
> >>
> >> Fix the following warnings:
> >>  warning: incorrect type in initializer (different address spaces)
> >>     expected unsigned short [noderef] __user *register __p
> >>     got unsigned short [usertype] *
> >>  warning: cast removes address space '__user' of expression
> >>
> >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> >> ---
> >>  arch/arm/kernel/traps.c | 10 +++++-----
> >>  1 file changed, 5 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> >> index 20b2db6dcd1ced7..34aa80c09c508c1 100644
> >> --- a/arch/arm/kernel/traps.c
> >> +++ b/arch/arm/kernel/traps.c
> >> @@ -188,9 +188,9 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
> >>                         }
> >>                 } else {
> >>                         if (thumb)
> >> -                               bad = get_user(val, &((u16 *)addr)[i]);
> >> +                               bad = get_user(val, &((u16 __user *)addr)[i]);
> >>                         else
> >> -                               bad = get_user(val, &((u32 *)addr)[i]);
> >> +                               bad = get_user(val, &((u32 __user *)addr)[i]);
> >>                 }
> >>
> >>                 if (!bad)
> >> @@ -455,15 +455,15 @@ asmlinkage void do_undefinstr(struct pt_regs *regs)
> >>         if (processor_mode(regs) == SVC_MODE) {
> >>  #ifdef CONFIG_THUMB2_KERNEL
> >>                 if (thumb_mode(regs)) {
> >> -                       instr = __mem_to_opcode_thumb16(((u16 *)pc)[0]);
> >> +                       instr = __mem_to_opcode_thumb16(((__force u16 *)pc)[0]);
> >
> > Shouldn't this be __user as well? (and below)
>
> unsigned int instr;
> void __user *pc;
>
> The __user can clear the warning, but a new warning will be generated.
>
> instr = __mem_to_opcode_thumb16(((u16 *)pc)[0]);
>       ^new                           ^old
>
> arch/arm/kernel/traps.c:473:33: warning: dereference of noderef expression
>

This is because dereferencing a __user pointer is not permitted.

So this code should be using get_kernel_nofault() here not a plain
dereference of PC. So better to fix that properly instead of papering
over it with a __force cast just to make sparse happy.


> >
> >>                         if (is_wide_instruction(instr)) {
> >>                                 u16 inst2;
> >> -                               inst2 = __mem_to_opcode_thumb16(((u16 *)pc)[1]);
> >> +                               inst2 = __mem_to_opcode_thumb16(((__force u16 *)pc)[1]);
> >>                                 instr = __opcode_thumb32_compose(instr, inst2);
> >>                         }
> >>                 } else
> >>  #endif
> >> -                       instr = __mem_to_opcode_arm(*(u32 *) pc);
> >> +                       instr = __mem_to_opcode_arm(*(__force u32 *) pc);
> >>         } else if (thumb_mode(regs)) {
> >>                 if (get_user(instr, (u16 __user *)pc))
> >>                         goto die_sig;
> >> --
> >> 2.25.1
> >>
> >>
> >> _______________________________________________
> >> linux-arm-kernel mailing list
> >> linux-arm-kernel@lists.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> > .
> >
>
> --
> Regards,
>   Zhen Lei