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SubjectRe: [PATCHv13 4/9] x86/boot/compressed: Handle unaccepted memory
On Fri, Jun 02, 2023 at 04:06:41PM +0200, Borislav Petkov wrote:
> On Thu, Jun 01, 2023 at 09:25:38PM +0300, Kirill A. Shutemov wrote:
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index 454757fbdfe5..749f0fe7e446 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -672,6 +672,28 @@ static bool process_mem_region(struct mem_vector *region,
> > }
> >
> > #ifdef CONFIG_EFI
> > +
> > +/*
> > + * Only EFI_CONVENTIONAL_MEMORY and EFI_UNACCEPTED_MEMORY (if supported) are
> > + * guaranteed to be free.
> > + *
> > + * It is more conservative in picking free memory than the EFI spec allows:
>
> "Pick free memory more conservatively than the EFI spec allows:
> EFI_BOOT_SERVICES_ ..."

Okay.

> > + *
> > + * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also free memory
> > + * and thus available to place the kernel image into, but in practice there's
> > + * firmware where using that memory leads to crashes.
>
> ... because that firmware still scratches into that memory or why?

I moved the existing comment. I don't have have any context beyond that.

Relevant commit: 0982adc74673 ("x86/boot/KASLR: Work around firmware bugs
by excluding EFI_BOOT_SERVICES_* and EFI_LOADER_* from KASLR's choice")

Ard, do you have anything to add here?

> > + */
> > +static inline bool memory_type_is_free(efi_memory_desc_t *md)
> > +{
> > + if (md->type == EFI_CONVENTIONAL_MEMORY)
> > + return true;
> > +
> > + if (md->type == EFI_UNACCEPTED_MEMORY)
> > + return IS_ENABLED(CONFIG_UNACCEPTED_MEMORY);
>
> Make it plan and simple:
>
> if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY) &&
> md->type == EFI_UNACCEPTED_MEMORY)
> return true;

I don't see why it is simpler. It looks unnecessary noisy to me.

But okay.

> > +
> > + return false;
> > +}
> > +
> > /*
> > * Returns true if we processed the EFI memmap, which we prefer over the E820
> > * table if it is available.
> > @@ -716,18 +738,7 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
> > for (i = 0; i < nr_desc; i++) {
> > md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
> >
> > - /*
> > - * Here we are more conservative in picking free memory than
> > - * the EFI spec allows:
> > - *
> > - * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
> > - * free memory and thus available to place the kernel image into,
> > - * but in practice there's firmware where using that memory leads
> > - * to crashes.
> > - *
> > - * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
> > - */
> > - if (md->type != EFI_CONVENTIONAL_MEMORY)
> > + if (!memory_type_is_free(md))
> > continue;
> >
> > if (efi_soft_reserve_enabled() &&
> > diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
> > index 67594fcb11d9..4ecf26576a77 100644
> > --- a/arch/x86/boot/compressed/mem.c
> > +++ b/arch/x86/boot/compressed/mem.c
> > @@ -1,9 +1,40 @@
> > // SPDX-License-Identifier: GPL-2.0-only
> >
> > #include "error.h"
> > +#include "misc.h"
> >
> > void arch_accept_memory(phys_addr_t start, phys_addr_t end)
> > {
> > /* Platform-specific memory-acceptance call goes here */
> > error("Cannot accept memory");
> > }
> > +
> > +void init_unaccepted_memory(void)
> > +{
> > + guid_t guid = LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID;
>
> An additional space after the "=".

Okay.

> > + struct efi_unaccepted_memory *unaccepted_table;
> > + unsigned long cfg_table_pa;
> > + unsigned int cfg_table_len;
> > + enum efi_type et;
> > + int ret;
> > +
> > + et = efi_get_type(boot_params);
> > + if (et == EFI_TYPE_NONE)
> > + return;
> > +
> > + ret = efi_get_conf_table(boot_params, &cfg_table_pa, &cfg_table_len);
> > + if (ret)
> > + error("EFI config table not found.");
>
> What's the point in erroring out here?

Configuration table suppose to be present, even if unaccepted memory is
not supported. Something is very wrong if it is missing.

I will downgrade it warn().

> > + unaccepted_table = (void *)efi_find_vendor_table(boot_params,
> > + cfg_table_pa,
> > + cfg_table_len,
> > + guid);
> > + if (!unaccepted_table)
> > + return;
> > +
> > + if (unaccepted_table->version != 1)
> > + error("Unknown version of unaccepted memory table\n");
> > +
> > + set_unaccepted_table(unaccepted_table);
>
> Why is this a function at all and not a simple assignment?

I wanted to keep unaccepted_table private to the libstub/unaccepted_memory.c.
The setter provides a good spot for documentation to guide unaccepted
memory enablers for other archs.

Still want replace it with direct assignment?

>
> > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > index 014ff222bf4b..36535a3753f5 100644
> > --- a/arch/x86/boot/compressed/misc.c
> > +++ b/arch/x86/boot/compressed/misc.c
> > @@ -455,6 +455,13 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
> > #endif
> >
> > debug_putstr("\nDecompressing Linux... ");
> > +
> > + if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY)) {
> > + debug_putstr("Accepting memory... ");
>
> This needs to happen...
>
> > + init_unaccepted_memory();
>
> ... after the init, after the init has parsed the config table and has
> found unaccepted memory.
>
> If not, you don't need to issue anything as that would be wrong.

Okay, I will make init_unaccepted_memory() return true if unaccepted
memory is present and hide defined it always-false for !UNACCEPTED_MEMORY.
So this hunk will look this way:

if (init_unaccepted_memory()) {
debug_putstr("Accepting memory... ");
accept_memory(__pa(output), __pa(output) + needed_size);
}

--
Kiryl Shutsemau / Kirill A. Shutemov

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