Messages in this thread | | | Subject | Re: [PATCH] arm64/traps: Avoid unnecessary kernel/user pointer conversion | From | Amit Kachhap <> | Date | Wed, 15 Sep 2021 19:26:55 +0530 |
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Hi,
On 9/14/21 9:30 PM, Mark Rutland wrote: > On Tue, Sep 14, 2021 at 08:57:42PM +0530, Amit Daniel Kachhap wrote: >> Annotating a pointer from kernel to __user and then back again might >> confuse sparse. In call_undef_hook() it can be avoided by not using the >> intermediate user pointer variable. > > When you say "might confuse sparse", does it complain today? If so, can > you include an example of what goes wrong?
No it does not give warning. The __force option silences the warning. My idea is to remove the unwanted __force annotations and not mix user and kernel pointers.
> >> Note: This patch adds no functional changes to code. >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> >> --- >> arch/arm64/kernel/traps.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c >> index b03e383d944a..357d10a8bbf5 100644 >> --- a/arch/arm64/kernel/traps.c >> +++ b/arch/arm64/kernel/traps.c >> @@ -404,7 +404,8 @@ static int call_undef_hook(struct pt_regs *regs) >> >> if (!user_mode(regs)) { >> __le32 instr_le; >> - if (get_kernel_nofault(instr_le, (__force __le32 *)pc)) >> + if (get_kernel_nofault(instr_le, >> + (__le32 *)instruction_pointer(regs))) > > Can we make `pc` an unsigned long, instead?
I think it can be done.
> > It'd be nice to handle all three cases consistently, even if that means > adding __force to the two user cases.
Agree with your suggestion. Even in the 2 user cases, __force may not be needed as the typecast will be from from unsigned long to user pointer.
BR, Amit > > Thanks, > Mark. > >> goto exit; >> instr = le32_to_cpu(instr_le); >> } else if (compat_thumb_mode(regs)) { >> -- >> 2.17.1 >>
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