[PATCH] arm64: idreg-override: Detect trailing "--" in __parse_cmdline()

[PATCH] arm64: idreg-override: Detect trailing "--" in __parse_cmdline()

[Thorsten Blum]

__parse_cmdline() detects "--" only if it is followed by whitespace.
However, at the end of the command line, it converts the dashes to
underscores and tries to match "__" as an option.

Detect trailing "--" directly instead of converting it to "__".

Fixes: dc3f5aae0638 ("arm64: idreg-override: Avoid parameq() and parameqn()")
Signed-off-by: Thorsten Blum <blum@kernel.org>
---
 arch/arm64/kernel/pi/idreg-override.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
index acaf56234973..38aa28d19650 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -352,8 +352,9 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
 
 		cmdline = skip_spaces(cmdline);
 
-		/* terminate on "--" appearing on the command line by itself */
-		if (cmdline[0] == '-' && cmdline[1] == '-' && isspace(cmdline[2]))
+		/* Stop at "--" appearing as a separate argument. */
+		if (cmdline[0] == '-' && cmdline[1] == '-' &&
+		    (!cmdline[2] || isspace(cmdline[2])))
 			return;
 
 		for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++) {

Re: [PATCH] arm64: idreg-override: Detect trailing "--" in __parse_cmdline()

[Catalin Marinas]

On Thu, Oct 15, 2026 at 06:10:54PM +0200, Thorsten Blum wrote:
> __parse_cmdline() detects "--" only if it is followed by whitespace.
> However, at the end of the command line, it converts the dashes to
> underscores and tries to match "__" as an option.
> 
> Detect trailing "--" directly instead of converting it to "__".
> 
> Fixes: dc3f5aae0638 ("arm64: idreg-override: Avoid parameq() and parameqn()")
> Signed-off-by: Thorsten Blum <blum@kernel.org>
> ---
>  arch/arm64/kernel/pi/idreg-override.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
> index acaf56234973..38aa28d19650 100644
> --- a/arch/arm64/kernel/pi/idreg-override.c
> +++ b/arch/arm64/kernel/pi/idreg-override.c
> @@ -352,8 +352,9 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
>  
>  		cmdline = skip_spaces(cmdline);
>  
> -		/* terminate on "--" appearing on the command line by itself */
> -		if (cmdline[0] == '-' && cmdline[1] == '-' && isspace(cmdline[2]))
> +		/* Stop at "--" appearing as a separate argument. */
> +		if (cmdline[0] == '-' && cmdline[1] == '-' &&
> +		    (!cmdline[2] || isspace(cmdline[2])))
>  			return;

I guess that's more of a cleanup. Does it actually fix anything to
deserve a Fixes tag? We skip an unnecessary lookup for "__" but there's
no functional difference.

-- 
Catalin

Re: [PATCH] arm64: idreg-override: Detect trailing "--" in __parse_cmdline()

[Thorsten Blum]

Hi Catalin,

On Tue, Oct 27, 2026 at 12:14:07PM +0000, Catalin Marinas wrote:
> On Thu, Oct 15, 2026 at 06:10:54PM +0200, Thorsten Blum wrote:
> > __parse_cmdline() detects "--" only if it is followed by whitespace.
> > However, at the end of the command line, it converts the dashes to
> > underscores and tries to match "__" as an option.
> > 
> > Detect trailing "--" directly instead of converting it to "__".
> > 
> > Fixes: dc3f5aae0638 ("arm64: idreg-override: Avoid parameq() and parameqn()")
> > Signed-off-by: Thorsten Blum <blum@kernel.org>
> > ---
> >  arch/arm64/kernel/pi/idreg-override.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
> > index acaf56234973..38aa28d19650 100644
> > --- a/arch/arm64/kernel/pi/idreg-override.c
> > +++ b/arch/arm64/kernel/pi/idreg-override.c
> > @@ -352,8 +352,9 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
> >  
> >  		cmdline = skip_spaces(cmdline);
> >  
> > -		/* terminate on "--" appearing on the command line by itself */
> > -		if (cmdline[0] == '-' && cmdline[1] == '-' && isspace(cmdline[2]))
> > +		/* Stop at "--" appearing as a separate argument. */
> > +		if (cmdline[0] == '-' && cmdline[1] == '-' &&
> > +		    (!cmdline[2] || isspace(cmdline[2])))
> >  			return;
> 
> I guess that's more of a cleanup. Does it actually fix anything to
> deserve a Fixes tag? We skip an unnecessary lookup for "__" but there's
> no functional difference.

Yes, it's a cleanup.

Functionally, the behavior is equivalent because it also happened to
work before. However, commit dc3f5aae0638 removed the explicit detection
of a trailing "--", so I added the Fixes tag mostly for provenance.

Thanks,
Thorsten

Re: [PATCH] arm64: idreg-override: Detect trailing "--" in __parse_cmdline()

[Catalin Marinas]

On Tue, Oct 27, 2026 at 03:49:45PM +0100, Thorsten Blum wrote:
> On Tue, Oct 27, 2026 at 12:14:07PM +0000, Catalin Marinas wrote:
> > On Thu, Oct 15, 2026 at 06:10:54PM +0200, Thorsten Blum wrote:
> > > __parse_cmdline() detects "--" only if it is followed by whitespace.
> > > However, at the end of the command line, it converts the dashes to
> > > underscores and tries to match "__" as an option.
> > > 
> > > Detect trailing "--" directly instead of converting it to "__".
> > > 
> > > Fixes: dc3f5aae0638 ("arm64: idreg-override: Avoid parameq() and parameqn()")
> > > Signed-off-by: Thorsten Blum <blum@kernel.org>
> > > ---
> > >  arch/arm64/kernel/pi/idreg-override.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
> > > index acaf56234973..38aa28d19650 100644
> > > --- a/arch/arm64/kernel/pi/idreg-override.c
> > > +++ b/arch/arm64/kernel/pi/idreg-override.c
> > > @@ -352,8 +352,9 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
> > >  
> > >  		cmdline = skip_spaces(cmdline);
> > >  
> > > -		/* terminate on "--" appearing on the command line by itself */
> > > -		if (cmdline[0] == '-' && cmdline[1] == '-' && isspace(cmdline[2]))
> > > +		/* Stop at "--" appearing as a separate argument. */
> > > +		if (cmdline[0] == '-' && cmdline[1] == '-' &&
> > > +		    (!cmdline[2] || isspace(cmdline[2])))
> > >  			return;
> > 
> > I guess that's more of a cleanup. Does it actually fix anything to
> > deserve a Fixes tag? We skip an unnecessary lookup for "__" but there's
> > no functional difference.
> 
> Yes, it's a cleanup.
> 
> Functionally, the behavior is equivalent because it also happened to
> work before. However, commit dc3f5aae0638 removed the explicit detection
> of a trailing "--", so I added the Fixes tag mostly for provenance.

Makes sense. We might make it a comment when applying rather than a
dedicated Fixes tag.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>