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SubjectRe: [PATCH 1/2] ARC: U-boot: check arguments paranoidly
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On Tue, 2019-02-12 at 16:45 +0000, Vineet Gupta wrote:
> On 2/12/19 7:39 AM, Eugeniy Paltsev wrote:
> > Handle U-boot arguments paranoidly:
> > * don't allow to pass unknown tag.
> > * try to use external device tree blob only if corresponding tag
> > (TAG_DTB) is set.
> > * check that magic number is correct.
> > * don't check uboot_tag if kernel build with no ARC_UBOOT_SUPPORT.
> >
> > NOTE:
> > If U-boot args are invalid we skip them and try to use embedded device
> > tree blob. We can't panic on invalid U-boot args as we really pass
> > invalid args due to bug in U-boot code.
> > This happens if we don't provide external DTB to U-boot and
> > don't set 'bootargs' U-boot environment variable (which is default
> > case at least for HSDK board) In that case we will pass
> > {r0 = 1 (bootargs in r2); r1 = 0; r2 = 0;} to linux which is invalid.
> >
> > NOTE:
> > We can safely check U-boot magic value (0x0) in linux passed via
> > r1 register as U-boot pass it from the beginning.
> >
> > While I'm at it refactor U-boot arguments handling code.
> >
> > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> > ---
> > arch/arc/kernel/head.S | 5 +--
> > arch/arc/kernel/setup.c | 92 +++++++++++++++++++++++++++++++++++--------------
> > 2 files changed, 69 insertions(+), 28 deletions(-)
> >
> > diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
> > index 8b90d25a15cc..fccea361e896 100644
> > --- a/arch/arc/kernel/head.S
> > +++ b/arch/arc/kernel/head.S
> > @@ -93,10 +93,11 @@ ENTRY(stext)
> > #ifdef CONFIG_ARC_UBOOT_SUPPORT
> > ; Uboot - kernel ABI
> > ; r0 = [0] No uboot interaction, [1] cmdline in r2, [2] DTB in r2
> > - ; r1 = magic number (board identity, unused as of now
> > + ; r1 = magic number (always zero as of now)
>
> This is technically changing the ABI - I think we don't need to enforce this -
> keep ignoring this

I think it's better to add this check:
* This check doesn't break backward compatibility. ARC U-boot pass zero to r1
from the beginnings, I specially checked this. So we doesn't change ABI,
we only document it ;)
* By adding this check we can cheap and easily minimize problems in JTAG case.

> > +
> > + if (use_embedded_dtb) {
> > machine_desc = setup_machine_fdt(__dtb_start);
> > if (!machine_desc)
> > panic("Embedded DT invalid\n");
> > + }
> >
> > - /*
> > - * If we are here, it is established that @uboot_arg didn't
> > - * point to DT blob. Instead if u-boot says it is cmdline,
> > - * append to embedded DT cmdline.
> > - * setup_machine_fdt() would have populated @boot_command_line
> > - */
>
> Don't drop this comment, specially the last line. If was tempted to move the cmd
> line processing before but this saved me since we rely on setup_machine_fdt()
> being called aprioiri.

Ok, will fix in v2

> > - if (uboot_tag == 1) {
> > - /* Ensure a whitespace between the 2 cmdlines */
> > - strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
> > - strlcat(boot_command_line, uboot_arg,
> > - COMMAND_LINE_SIZE);
> > - }
> > + if (append_cmdline) {
> > + /* Ensure a whitespace between the 2 cmdlines */
> > + strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
> > + strlcat(boot_command_line, (char *)uboot_arg, COMMAND_LINE_SIZE);
> > }
> > +}
> > +
> > +void __init setup_arch(char **cmdline_p)
> > +{
> > + handle_uboot_args();
> >
> > /* Save unparsed command line copy for /proc/cmdline */
> > *cmdline_p = boot_command_line;
>
>
--
Eugeniy Paltsev
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