Re: [PATCH v4 4/4] efi: Fix handling of multiple efi_fake_mem= entries

[Dave Young]

On 01/06/20 at 04:40pm, Dan Williams wrote:
> Dave noticed that when specifying multiple efi_fake_mem= entries only
> the last entry was successfully being reflected in the efi memory map.
> This is due to the fact that the efi_memmap_insert() is being called
> multiple times, but on successive invocations the insertion should be
> applied to the last new memmap rather than the original map at
> efi_fake_memmap() entry.
> 
> Rework efi_fake_memmap() to install the new memory map after each
> efi_fake_mem= entry is parsed.
> 
> This also fixes an issue in efi_fake_memmap() that caused it to litter
> emtpy entries into the end of the efi memory map. An empty entry causes
> efi_memmap_insert() to attempt more memmap splits / copies than
> efi_memmap_split_count() accounted for when sizing the new map. When
> that happens efi_memmap_insert() may overrun its allocation, and if you
> are lucky will spill over to an unmapped page leading to crash
> signature like the following rather than silent corruption:
> 
>     BUG: unable to handle page fault for address: ffffffffff281000
>     [..]
>     RIP: 0010:efi_memmap_insert+0x11d/0x191
>     [..]
>     Call Trace:
>      ? bgrt_init+0xbe/0xbe
>      ? efi_arch_mem_reserve+0x1cb/0x228
>      ? acpi_parse_bgrt+0xa/0xd
>      ? acpi_table_parse+0x86/0xb8
>      ? acpi_boot_init+0x494/0x4e3
>      ? acpi_parse_x2apic+0x87/0x87
>      ? setup_acpi_sci+0xa2/0xa2
>      ? setup_arch+0x8db/0x9e1
>      ? start_kernel+0x6a/0x547
>      ? secondary_startup_64+0xb6/0xc0
> 
> Commit af1648984828 "x86/efi: Update e820 with reserved EFI boot
> services data to fix kexec breakage" is listed in Fixes: since it
> introduces more occurrences where efi_memmap_insert() is invoked after
> an efi_fake_mem= configuration has been parsed. Previously the side
> effects of vestigial empty entries were benign, but with commit
> af1648984828 that follow-on efi_memmap_insert() invocation triggers
> efi_memmap_insert() overruns.
> 
> Fixes: 0f96a99dab36 ("efi: Add 'efi_fake_mem' boot option")
> Fixes: af1648984828 ("x86/efi: Update e820 with reserved EFI boot services...")

A nitpick for the Fixes flags, as I replied in the thread below:
https://lore.kernel.org/linux-efi/CAPcyv4jLxqPaB22Ao9oV31Gm=b0+Phty+Uz33Snex4QchOUb0Q@xxxxxxxxxxxxxx/T/#m2bb2dd00f7715c9c19ccc48efef0fcd5fdb626e7

I reproduced two other panics without the patches applied, so this issue
is not caused by either of the commits, maybe just drop the Fixes.

> Link: https://lore.kernel.org/r/20191231014630.GA24942@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: Dave Young <dyoung@xxxxxxxxxx>
> Cc: Taku Izumi <izumi.taku@xxxxxxxxxxxxxx>
> Cc: Michael Weiser <michael@xxxxxxxxxxxxxxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  drivers/firmware/efi/fake_mem.c |   31 ++++++++++++++++---------------
>  drivers/firmware/efi/memmap.c   |    2 +-
>  include/linux/efi.h             |    2 ++
>  3 files changed, 19 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/firmware/efi/fake_mem.c b/drivers/firmware/efi/fake_mem.c
> index a8d20568d532..6e0f34a38171 100644
> --- a/drivers/firmware/efi/fake_mem.c
> +++ b/drivers/firmware/efi/fake_mem.c
> @@ -34,25 +34,16 @@ static int __init cmp_fake_mem(const void *x1, const void *x2)
>  	return 0;
>  }
>  
> -void __init efi_fake_memmap(void)
> +static void __init efi_fake_range(struct efi_mem_range *efi_range)
>  {
>  	struct efi_memory_map_data data = { 0 };
>  	int new_nr_map = efi.memmap.nr_map;
>  	efi_memory_desc_t *md;
>  	void *new_memmap;
> -	int i;
> -
> -	if (!efi_enabled(EFI_MEMMAP) || !nr_fake_mem)
> -		return;
>  
>  	/* count up the number of EFI memory descriptor */
> -	for (i = 0; i < nr_fake_mem; i++) {
> -		for_each_efi_memory_desc(md) {
> -			struct range *r = &efi_fake_mems[i].range;
> -
> -			new_nr_map += efi_memmap_split_count(md, r);
> -		}
> -	}
> +	for_each_efi_memory_desc(md)
> +		new_nr_map += efi_memmap_split_count(md, &efi_range->range);

For this part, although I still have some concerns, but since I'm not
100% clear about it, maybe just leave it as you do, and see if it is
good to Ard.

>  
>  	/* allocate memory for new EFI memmap */
>  	if (efi_memmap_alloc(new_nr_map, &data) != 0)
> @@ -61,17 +52,27 @@ void __init efi_fake_memmap(void)
>  	/* create new EFI memmap */
>  	new_memmap = early_memremap(data.phys_map, data.size);
>  	if (!new_memmap) {
> -		memblock_free(data.phys_map, data.size);
> +		__efi_memmap_free(data.phys_map, data.size, data.flags);
>  		return;
>  	}
>  
> -	for (i = 0; i < nr_fake_mem; i++)
> -		efi_memmap_insert(&efi.memmap, new_memmap, &efi_fake_mems[i]);
> +	efi_memmap_insert(&efi.memmap, new_memmap, efi_range);
>  
>  	/* swap into new EFI memmap */
>  	early_memunmap(new_memmap, data.size);
>  
>  	efi_memmap_install(&data);
> +}
> +
> +void __init efi_fake_memmap(void)
> +{
> +	int i;
> +
> +	if (!efi_enabled(EFI_MEMMAP) || !nr_fake_mem)
> +		return;
> +
> +	for (i = 0; i < nr_fake_mem; i++)
> +		efi_fake_range(&efi_fake_mems[i]);
>  
>  	/* print new EFI memmap */
>  	efi_print_memmap();
> diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
> index bffa320d2f9a..1b6a4aa78a09 100644
> --- a/drivers/firmware/efi/memmap.c
> +++ b/drivers/firmware/efi/memmap.c
> @@ -29,7 +29,7 @@ static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
>  	return PFN_PHYS(page_to_pfn(p));
>  }
>  
> -static void __init __efi_memmap_free(u64 phys, unsigned long size, unsigned long flags)
> +void __init __efi_memmap_free(u64 phys, unsigned long size, unsigned long flags)
>  {
>  	if (flags & EFI_MEMMAP_MEMBLOCK) {
>  		if (slab_is_available())
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 416eac01b1a1..539e81c942dc 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1062,6 +1062,8 @@ extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
>  
>  extern int __init efi_memmap_alloc(unsigned int num_entries,
>  				   struct efi_memory_map_data *data);
> +extern void __efi_memmap_free(u64 phys, unsigned long size,
> +			      unsigned long flags);
>  extern int __init efi_memmap_init_early(struct efi_memory_map_data *data);
>  extern int __init efi_memmap_init_late(phys_addr_t addr, unsigned long size);
>  extern void __init efi_memmap_unmap(void);
> 

Thanks
Dave