linux-kernel - Re: [tip: efi/core] efi: Support for MOK variable config table

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Message-ID: <20200921155551.GA1470@zn.tnic>
Date:   Mon, 21 Sep 2020 17:55:51 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Lenny Szubowicz <lszubowi@...hat.com>
Cc:     linux-tip-commits@...r.kernel.org,
        Lenny Szubowicz <lszubowi@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [tip: efi/core] efi: Support for MOK variable config table

On Fri, Sep 18, 2020 at 08:30:54AM -0000, tip-bot2 for Lenny Szubowicz wrote:
> +void __init efi_mokvar_table_init(void)
> +{
> +	efi_memory_desc_t md;
> +	u64 end_pa;
> +	void *va = NULL;
> +	size_t cur_offset = 0;
> +	size_t offset_limit;
> +	size_t map_size = 0;
> +	size_t map_size_needed = 0;
> +	size_t size;
> +	struct efi_mokvar_table_entry *mokvar_entry;
> +	int err = -EINVAL;
> +
> +	if (!efi_enabled(EFI_MEMMAP))
> +		return;
> +
> +	if (efi.mokvar_table == EFI_INVALID_TABLE_ADDR)
> +		return;
> +	/*
> +	 * The EFI MOK config table must fit within a single EFI memory
> +	 * descriptor range.
> +	 */
> +	err = efi_mem_desc_lookup(efi.mokvar_table, &md);
> +	if (err) {
> +		pr_warn("EFI MOKvar config table is not within the EFI memory map\n");
> +		return;
> +	}
> +	end_pa = efi_mem_desc_end(&md);
> +	if (efi.mokvar_table >= end_pa) {
> +		pr_err("EFI memory descriptor containing MOKvar config table is invalid\n");
> +		return;
> +	}
> +	offset_limit = end_pa - efi.mokvar_table;
> +	/*
> +	 * Validate the MOK config table. Since there is no table header
> +	 * from which we could get the total size of the MOK config table,
> +	 * we compute the total size as we validate each variably sized
> +	 * entry, remapping as necessary.
> +	 */
> +	while (cur_offset + sizeof(*mokvar_entry) <= offset_limit) {
> +		mokvar_entry = va + cur_offset;
> +		map_size_needed = cur_offset + sizeof(*mokvar_entry);
> +		if (map_size_needed > map_size) {
> +			if (va)
> +				early_memunmap(va, map_size);
> +			/*
> +			 * Map a little more than the fixed size entry
> +			 * header, anticipating some data. It's safe to
> +			 * do so as long as we stay within current memory
> +			 * descriptor.
> +			 */
> +			map_size = min(map_size_needed + 2*EFI_PAGE_SIZE,
> +				       offset_limit);

i386 allmodconfig build gives here:

In file included from ./arch/x86/include/asm/percpu.h:27:0,
                 from ./arch/x86/include/asm/current.h:6,
                 from ./arch/x86/include/asm/processor.h:17,
                 from ./arch/x86/include/asm/timex.h:5,
                 from ./include/linux/timex.h:65,
                 from ./include/linux/time32.h:13,
                 from ./include/linux/time.h:73,
                 from ./include/linux/efi.h:17,
                 from drivers/firmware/efi/mokvar-table.c:35:
drivers/firmware/efi/mokvar-table.c: In function ‘efi_mokvar_table_init’:
./include/linux/kernel.h:850:29: warning: comparison of distinct pointer types lacks a cast
   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                             ^
./include/linux/kernel.h:864:4: note: in expansion of macro ‘__typecheck’
   (__typecheck(x, y) && __no_side_effects(x, y))
    ^~~~~~~~~~~
./include/linux/kernel.h:874:24: note: in expansion of macro ‘__safe_cmp’
  __builtin_choose_expr(__safe_cmp(x, y), \
                        ^~~~~~~~~~
./include/linux/kernel.h:883:19: note: in expansion of macro ‘__careful_cmp’
 #define min(x, y) __careful_cmp(x, y, <)
                   ^~~~~~~~~~~~~
drivers/firmware/efi/mokvar-table.c:149:15: note: in expansion of macro ‘min’
    map_size = min(map_size_needed + 2*EFI_PAGE_SIZE,
               ^~~

-- 
Regards/Gruss,
    Boris.

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