On Thu, Feb 25, 2021 at 01:53:56PM +0000, Marc Zyngier wrote:
> On Thu, 25 Feb 2021 12:59:20 +0000,
> Will Deacon <will@xxxxxxxxxx> wrote:
> >
> > The built-in kernel commandline (CONFIG_CMDLINE) can be configured in
> > three different ways:
> >
> > 1. CMDLINE_FORCE: Use CONFIG_CMDLINE instead of any bootloader args
> > 2. CMDLINE_EXTEND: Append the bootloader args to CONFIG_CMDLINE
> > 3. CMDLINE_FROM_BOOTLOADER: Only use CONFIG_CMDLINE if there aren't
> > any bootloader args.
> >
> > The early cmdline parsing to detect idreg overrides gets (2) and (3)
> > slightly wrong: in the case of (2) the bootloader args are parsed first
> > and in the case of (3) the CMDLINE is always parsed.
> >
> > Fix these issues by moving the bootargs parsing out into a helper
> > function and following the same logic as that used by the EFI stub.
> >
> > Cc: Marc Zyngier <maz@xxxxxxxxxx>
> > Fixes: 33200303553d ("arm64: cpufeature: Add an early command-line cpufeature override facility")
> > Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> > ---
> > arch/arm64/kernel/idreg-override.c | 44 +++++++++++++++++-------------
> > 1 file changed, 25 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> > index dffb16682330..cc071712c6f9 100644
> > --- a/arch/arm64/kernel/idreg-override.c
> > +++ b/arch/arm64/kernel/idreg-override.c
> > @@ -163,33 +163,39 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
> > } while (1);
> > }
> >
> > -static __init void parse_cmdline(void)
> > +static __init const u8 *get_bootargs_cmdline(void)
> > {
> > - if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
> > - const u8 *prop;
> > - void *fdt;
> > - int node;
> > + const u8 *prop;
> > + void *fdt;
> > + int node;
> >
> > - fdt = get_early_fdt_ptr();
> > - if (!fdt)
> > - goto out;
> > + fdt = get_early_fdt_ptr();
> > + if (!fdt)
> > + return NULL;
> >
> > - node = fdt_path_offset(fdt, "/chosen");
> > - if (node < 0)
> > - goto out;
> > + node = fdt_path_offset(fdt, "/chosen");
> > + if (node < 0)
> > + return NULL;
> >
> > - prop = fdt_getprop(fdt, node, "bootargs", NULL);
> > - if (!prop)
> > - goto out;
> > + prop = fdt_getprop(fdt, node, "bootargs", NULL);
> > + if (!prop)
> > + return NULL;
> >
> > - __parse_cmdline(prop, true);
> > + return strlen(prop) ? prop : NULL;
> > +}
> >
> > - if (!IS_ENABLED(CONFIG_CMDLINE_EXTEND))
> > - return;
> > +static __init void parse_cmdline(void)
> > +{
> > + const u8 *prop = get_bootargs_cmdline();
> > +
> > + if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||
> > + IS_ENABLED(CONFIG_CMDLINE_FORCE) ||
> > + !prop) {
>
> The logic hurts, but I think I grok it now. The last term is actually
> a reduction of
>
> (IS_ENABLED(CONFIG_CMDLINE_FROM_BOOTLOADER) && !prop)
>
> and we know for sure that if none of the other two terms are true,
> then CMDLINE_FROM_BOOTLOADER *must* be enabled.
Yes, with one gotcha: when CONFIG_CMDLINE is "", I don't think any of the
CONFIG_CMDLINE_* are set, but the behaviour ends up being the same as
CMDLINE_FROM_BOOTLOADER.
>
> > + __parse_cmdline(CONFIG_CMDLINE, true);
> > }
> >
> > -out:
> > - __parse_cmdline(CONFIG_CMDLINE, true);
> > + if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
> > + __parse_cmdline(prop, true);
> > }
> >
> > /* Keep checkers quiet */
>
> I don't think we need to backport anything to stable for the nokaslr
> handling, do we?
No, I don't think so. There isn't a "kaslr" or "nonokaslr", so the ordering
doesn't matter afaict.
> Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Cheers!
Will
