linux-kernel - Re: [PATCH stable v6.6] riscv: kprobes: Fix wrong lengths passed to patch_text

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Message-ID: <20250429164614.g3w8JJAk@linutronix.de>
Date: Tue, 29 Apr 2025 18:48:21 +0200
From: Nam Cao <namcao@...utronix.de>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: stable@...r.kernel.org, Kai Zhang <zhangkai@...as.ac.cn>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Samuel Holland <samuel.holland@...ive.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH stable v6.6] riscv: kprobes: Fix wrong lengths passed to
 patch_text_nosync()

On Tue, Apr 29, 2025 at 06:31:09PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Apr 29, 2025 at 06:14:18PM +0200, Nam Cao wrote:
> > Unlike patch_text(), patch_text_nosync() takes the length in bytes, not
> > number of instructions. It is therefore wrong for arch_prepare_ss_slot() to
> > pass length=1 while patching one instruction.
> > 
> > This bug was introduced by commit b1756750a397 ("riscv: kprobes: Use
> > patch_text_nosync() for insn slots"). It has been fixed upstream by commit
> > 51781ce8f448 ("riscv: Pass patch_text() the length in bytes"). However,
> > beside fixing this bug, this commit does many other things, making it
> > unsuitable for backporting.
> 
> We would almost always want the original commit, why not just send that
> instead?  What is wrong with it being in here as-is?

The original commit is probably fine. But I'm paranoid, because it is not
completely obvious whether the original commit would break something else
in v6.6. Because, as mentioned, it does more than just fixing the bug.

Best regards,
Nam