linux-kernel - Re: [PATCH 1/3] efi/libstub: fix efi_parse_options() ignoring the default command line

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Message-ID: <CAMj1kXFfsjPy9UxtC4f6n+FBBYRdyGw6h0b9fkn3_NDxTL7nPg@mail.gmail.com>
Date: Sat, 12 Oct 2024 15:15:34 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Jonathan Marek <jonathan@...ek.ca>
Cc: linux-efi@...r.kernel.org, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>, 
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] efi/libstub: fix efi_parse_options() ignoring the
 default command line

On Sat, 12 Oct 2024 at 13:58, Jonathan Marek <jonathan@...ek.ca> wrote:
>
> On 10/12/24 3:46 AM, Ard Biesheuvel wrote:
> > Hi Jonathan,
> >
> > Please use a cover letter when sending more than a single patch.
> >
> > On Sat, 12 Oct 2024 at 00:51, Jonathan Marek <jonathan@...ek.ca> wrote:
> >>
> >> efi_convert_cmdline() always returns a size of at least 1 because it counts
> >> the NUL terminator, so the "cmdline_size == 0" condition is not possible.
> >>
> >> Change it to compare against 1 to get the intended behavior: to use
> >> CONFIG_CMDLINE when load_options_size is 0.
> >>
> >> Fixes: 60f38de7a8d4 ("efi/libstub: Unify command line param parsing")
> >> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> >> ---
> >>   drivers/firmware/efi/libstub/efi-stub.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/firmware/efi/libstub/efi-stub.c b/drivers/firmware/efi/libstub/efi-stub.c
> >> index 958a680e0660d..709ae2d41a632 100644
> >> --- a/drivers/firmware/efi/libstub/efi-stub.c
> >> +++ b/drivers/firmware/efi/libstub/efi-stub.c
> >> @@ -129,7 +129,7 @@ efi_status_t efi_handle_cmdline(efi_loaded_image_t *image, char **cmdline_ptr)
> >>
> >>          if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||
> >>              IS_ENABLED(CONFIG_CMDLINE_FORCE) ||
> >> -           cmdline_size == 0) {
> >> +           cmdline_size == 1) {
> >
> > I'd prefer it if we could keep the weirdness local to
> > efi_convert_cmdline(). Would the below fix things too?
> >
> > --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> > +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> > @@ -395,9 +395,7 @@
> >                  }
> >          }
> >
> > -       options_bytes++;        /* NUL termination */
> > -
> > -       status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, options_bytes,
> > +       status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, options_bytes + 1,
> >                               (void **)&cmdline_addr);
> >          if (status != EFI_SUCCESS)
> >                  return NULL;
> >
> > Note that the only other caller of efi_convert_cmdline() in x86-stub.c
> > ignores this value entirely.
> >
>
> Just changing this would just make things more broken, the following
> snprintf would remove the last character of the command line because it
> uses options_bytes.
>

Ugh, you're right. So just use options_bytes - 1 in the assignment then.

> Since this patch has a Fixes: tag, I wanted to make the fix as simple as
> possible. If you think comparing the size to 1 is "weird", the fix could
> instead check if cmdline[0] is non-NUL (or just strlen(cmdline)==0 if
> you don't like that either).
>

Checking the value of the first byte is reasonable I think.

> And then my followup cleanup patch can just remove the cmd_line_len
> argument from efi_convert_cmdline().

Yes that would be fine - it is not really useful in any case.