Re: [PATCH] x86/intel/quark: Remove lock bit around kernel IMR

From: Andy Shevchenko
Date: Thu Jan 21 2016 - 13:44:22 EST

On Thu, Jan 21, 2016 at 4:05 PM, Bryan O'Donoghue
<pure.logic@xxxxxxxxxxxxxxxxx> wrote:
> Currently when setting up an IMR around the kernel .text area we lock that
> IMR, preventing further modification. While superficially this appears to
> be the right thing to do, in fact this doesn't account for a legitimate
> change in the memory map such as when running through kexec. In such a
> scenario a second kernel can have a different size and location to it's
> predecessor and can view some of the memory occupied by its predecessor as
> legitimately usable RAM. This RAM can then be allocated to DMA agents
> within the system and trigger an IMR violation.
> The solution to this situation is to keep the kernel .text section IMR lock
> bit false. This means that a subsequent kernel will boot and can tear-down
> an existing IMR, while still setting up an IMR around its own .text
> section.

Like I said you privately it would be nice to have a knob how to behave.

My idea is to provide kernel command line imr= and supply imr=lock
when user wants to boot kernel locked.

Optionally: add a warning if imr=lock and kernel build with kexec that
might bring issues
Optionally: add a kernel config option to boot always in locked mode
(should depend on !KEXEC)

> Signed-off-by: Bryan O'Donoghue <pure.logic@xxxxxxxxxxxxxxxxx>
> Reported-by: Andriy Shevchenko <andriy.shevchenko@xxxxxxxxx>
> ---
> arch/x86/platform/intel-quark/imr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/arch/x86/platform/intel-quark/imr.c b/arch/x86/platform/intel-quark/imr.c
> index c1bdafa..1c43639 100644
> --- a/arch/x86/platform/intel-quark/imr.c
> +++ b/arch/x86/platform/intel-quark/imr.c
> @@ -591,7 +591,7 @@ static void __init imr_fixup_memmap(struct imr_device *idev)
> * from the beginning of the .text secton to the end of the
> * .rodata section as one physically contiguous block.
> */
> - ret = imr_add_range(base, size, IMR_CPU, IMR_CPU, true);
> + ret = imr_add_range(base, size, IMR_CPU, IMR_CPU, false);
> if (ret < 0) {
> pr_err("unable to setup IMR for kernel: (%p - %p)\n",
> &_text, &__end_rodata);
> --
> 2.5.0

With Best Regards,
Andy Shevchenko