[PATCH v2] arm64/traps: Avoid unnecessary kernel/user pointer conversion

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 <redacted>
---
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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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 <redacted>

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.

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On Fri, 17 Sep 2021 11:28:11 +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.

[...]

Applied to arm64 (for-next/misc), thanks!

[1/1] arm64/traps: Avoid unnecessary kernel/user pointer conversion
      https://git.kernel.org/arm64/c/f5b650f887f3

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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