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Message-ID: <bf52c912-7a05-3f66-31a0-50131bf0c810@huawei.com>
Date: Thu, 13 Oct 2022 19:34:17 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
CC: Ard Biesheuvel <ardb@...nel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] ARM: Fix some check warnings of tool sparse
On 2022/10/13 18:51, Russell King (Oracle) wrote:
> On Tue, Oct 11, 2022 at 10:29:58AM +0800, Leizhen (ThunderTown) wrote:
>> On 2022/10/10 19:06, Ard Biesheuvel wrote:
>>> On Mon, 10 Oct 2022 at 12:58, Leizhen (ThunderTown)
>>> <thunder.leizhen@...wei.com> wrote:
>>>> On 2022/10/10 18:20, Ard Biesheuvel wrote:
>>>>> On Mon, 10 Oct 2022 at 11:56, Zhen Lei <thunder.leizhen@...wei.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@...wei.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.
>>
>> How about:
>> @@ -451,9 +451,9 @@ int call_undef_hook(struct pt_regs *regs, unsigned int instr)
>> asmlinkage void do_undefinstr(struct pt_regs *regs)
>> {
>> unsigned int instr;
>> - void __user *pc;
>> + void *pc;
>>
>> - pc = (void __user *)instruction_pointer(regs);
>> + pc = (void *)instruction_pointer(regs);
>>
>> if (processor_mode(regs) == SVC_MODE) {
>> #ifdef CONFIG_THUMB2_KERNEL
>> @@ -497,7 +497,7 @@ asmlinkage void do_undefinstr(struct pt_regs *regs)
>> }
>> #endif
>> arm_notify_die("Oops - undefined instruction", regs,
>> - SIGILL, ILL_ILLOPC, pc, 0, 6);
>> + SIGILL, ILL_ILLOPC, (void __user *)pc, 0, 6);
>> }
>> NOKPROBE_SYMBOL(do_undefinstr)
>>
>>
>> The 'pc' may come from kernel or user. And I found that all the get_user()
>> calls have already done type casts to the pc, except arm_notify_die().
>> I think the above changes are reasonable.
>
> If we're going to do that, lets do it properly - I think the above would
> need some __force usage to stop sparse complaining, whereas I don't
No need to add __force. I sent it after testing.
$ cat .config | grep THUMB2
CONFIG_THUMB2_KERNEL=y
$ make C=2 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- arch/arm/kernel/traps.o
CHECK scripts/mod/empty.c
CALL scripts/checksyscalls.sh
CHECK arch/arm/kernel/traps.c
arch/arm/kernel/traps.c:97:6: warning: symbol 'dump_backtrace_stm' was not declared. Should it be static?
arch/arm/kernel/traps.c:451:17: warning: symbol 'do_undefinstr' was not declared. Should it be static?
arch/arm/kernel/traps.c:516:39: warning: symbol 'handle_fiq_as_nmi' was not declared. Should it be static?
arch/arm/kernel/traps.c:535:17: warning: symbol 'bad_mode' was not declared. Should it be static?
arch/arm/kernel/traps.c:608:16: warning: symbol 'arm_syscall' was not declared. Should it be static?
arch/arm/kernel/traps.c:734:1: warning: symbol 'baddataabort' was not declared. Should it be static?
arch/arm/kernel/traps.c:774:17: warning: symbol '__div0' was not declared. Should it be static?
arch/arm/kernel/traps.c:781:6: warning: symbol 'abort' was not declared. Should it be static?
arch/arm/kernel/traps.c:905:12: warning: symbol 'overflow_stack_ptr' was not declared. Should it be static?
arch/arm/kernel/traps.c:922:17: warning: symbol 'handle_bad_stack' was not declared. Should it be static?
> think this will (untested):
>
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 3f468ac98592..827cbc022900 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -449,36 +449,45 @@ int call_undef_hook(struct pt_regs *regs, unsigned int instr)
> asmlinkage void do_undefinstr(struct pt_regs *regs)
> {
> unsigned int instr;
> - void __user *pc;
> + unsigned long pc;
>
> - pc = (void __user *)instruction_pointer(regs);
> + pc = instruction_pointer(regs);
>
> if (processor_mode(regs) == SVC_MODE) {
> -#ifdef CONFIG_THUMB2_KERNEL
> - if (thumb_mode(regs)) {
> - instr = __mem_to_opcode_thumb16(((u16 *)pc)[0]);
> + if (IS_ENABLED(CONFIG_THUMB2_KERNEL) && thumb_mode(regs)) {
> + u16 *tpc = (u16 *)pc;
> +
> + instr = __mem_to_opcode_thumb16(tpc[0]);
> if (is_wide_instruction(instr)) {
> u16 inst2;
> - inst2 = __mem_to_opcode_thumb16(((u16 *)pc)[1]);
> +
> + inst2 = __mem_to_opcode_thumb16(tpc[1]);
> instr = __opcode_thumb32_compose(instr, inst2);
> }
> - } else
> -#endif
> - instr = __mem_to_opcode_arm(*(u32 *) pc);
> + } else {
> + u32 *apc = (u32 *)pc;
> +
> + instr = __mem_to_opcode_arm(*apc);
> + }
> } else if (thumb_mode(regs)) {
> - if (get_user(instr, (u16 __user *)pc))
> + u16 __user *tpc = (u16 __user *)pc;
> +
> + if (get_user(instr, tpc))
> goto die_sig;
> instr = __mem_to_opcode_thumb16(instr);
> if (is_wide_instruction(instr)) {
> unsigned int instr2;
> - if (get_user(instr2, (u16 __user *)pc+1))
> + if (get_user(instr2, tpc + 1))
> goto die_sig;
> instr2 = __mem_to_opcode_thumb16(instr2);
> instr = __opcode_thumb32_compose(instr, instr2);
> }
> } else {
> - if (get_user(instr, (u32 __user *)pc))
> + u32 __user *apc = (u32 __user *)pc;
> +
> + if (get_user(instr, apc))
> goto die_sig;
> +
> instr = __mem_to_opcode_arm(instr);
> }
>
> @@ -495,7 +504,7 @@ asmlinkage void do_undefinstr(struct pt_regs *regs)
> }
> #endif
> arm_notify_die("Oops - undefined instruction", regs,
> - SIGILL, ILL_ILLOPC, pc, 0, 6);
> + SIGILL, ILL_ILLOPC, (void __user *)pc, 0, 6);
> }
> NOKPROBE_SYMBOL(do_undefinstr)
>
>
--
Regards,
Zhen Lei
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