Messages in this thread | | | Date | Mon, 10 Oct 2022 17:17:55 +0100 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH v2 1/2] ARM: Fix some check warnings of tool sparse |
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On Mon, Oct 10, 2022 at 06:14:56PM +0200, Ard Biesheuvel wrote: > On Mon, 10 Oct 2022 at 18:08, Russell King (Oracle) > <linux@armlinux.org.uk> wrote: > > > > On Mon, Oct 10, 2022 at 01:06:19PM +0200, Ard Biesheuvel wrote: > > > 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. > > > > Why? We won't get here unless the PC can be dereferenced. If it's not > > able to be dereferenced, then we'd be dealing with a prefetch abort. > > > > If that is guaranteed (i.e., there is no way we might be racing with a > module unload on another CPU or something like that), then I agree > that dereferencing PC is fine.
If we get here for an instruction in a module that's being unloaded, we have way bigger problems. We shouldn't be executing code in a module being unloaded in the first place. That becomes a case of "deserves to oops".
The more likely case would be a prefetch abort when the page is unmapped. You'd have to try pretty hard to get an undef to race with a module unload.
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