From: Mark Rutland <mark.rutland@arm.com>
To: Amit Daniel Kachhap <amit.kachhap@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH v2] arm64/traps: Avoid unnecessary kernel/user pointer conversion
Date: Fri, 17 Sep 2021 10:36:28 +0100 [thread overview]
Message-ID: <20210917093628.GB75427@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20210917055811.22341-1-amit.kachhap@arm.com>
On Fri, Sep 17, 2021 at 11:28:11AM +0530, Amit Daniel Kachhap wrote:
> Annotating a pointer from kernel to __user and then back again requires
> an extra __force annotation to silent sparse warning. In call_undef_hook()
> this unnecessary complexity can be avoided by modifying the intermediate
> user pointer to unsigned long.
>
> This way there is no inter-changeable use of user and kernel pointers
> and the code is consistent.
>
> 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>
I like that this clarifies that `pc` is not necessarily a user pointer,
and this makes the relevant lines shorter and eaier to read, so FWIW:
Acked-by: Mark Rutland <mark.rutland@arm.com>
Thanks,
Mark.
> ---
> Changes from v1:
> * Instead of directly using instruction_pointer() for kernel pointers,
> modified the pc type from void __user * to unsigned long as suggested
> by Mark Rutland.
>
> arch/arm64/kernel/traps.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index b03e383d944a..09236751283e 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -400,11 +400,11 @@ static int call_undef_hook(struct pt_regs *regs)
> unsigned long flags;
> u32 instr;
> int (*fn)(struct pt_regs *regs, u32 instr) = NULL;
> - void __user *pc = (void __user *)instruction_pointer(regs);
> + unsigned long pc = instruction_pointer(regs);
>
> if (!user_mode(regs)) {
> __le32 instr_le;
> - if (get_kernel_nofault(instr_le, (__force __le32 *)pc))
> + if (get_kernel_nofault(instr_le, (__le32 *)pc))
> goto exit;
> instr = le32_to_cpu(instr_le);
> } else if (compat_thumb_mode(regs)) {
> --
> 2.17.1
>
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next prev parent reply other threads:[~2021-09-17 9:38 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-17 5:58 [PATCH v2] arm64/traps: Avoid unnecessary kernel/user pointer conversion Amit Daniel Kachhap
2021-09-17 9:36 ` Mark Rutland [this message]
2021-09-29 17:48 ` Will Deacon
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