linux-kernel - arm64/efi handling of persistent memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <94D0CD8314A33A4D9D801C0FE68B40295BEBD864@G9W0745.americas.hpqcorp.net>
Date:	Fri, 18 Dec 2015 01:33:25 +0000
From:	"Elliott, Robert (Persistent Memory)" <elliott@....com>
To:	"catalin.marinas@....com" <catalin.marinas@....com>,
	"will.deacon@....com" <will.deacon@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>
CC:	"matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>,
	"leif.lindholm@...aro.org" <leif.lindholm@...aro.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"Kani, Toshimitsu" <toshi.kani@....com>,
	"Knippers, Linda" <linda.knippers@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: arm64/efi handling of persistent memory

Similar to the questions about the arm64 efi boot stub
handing persistent memory, some of the arm64 kernel code 
looks fishy.

In arch/arm64/kernel/efi.c:

static int __init is_normal_ram(efi_memory_desc_t *md)
{
        if (md->attribute & EFI_MEMORY_WB)
                return 1;
        return 0;
}

static __init int is_reserve_region(efi_memory_desc_t *md)
{
        switch (md->type) {
        case EFI_LOADER_CODE:
        case EFI_LOADER_DATA:
        case EFI_BOOT_SERVICES_CODE:
        case EFI_BOOT_SERVICES_DATA:
        case EFI_CONVENTIONAL_MEMORY:
        case EFI_PERSISTENT_MEMORY:
                return 0;
        default:
                break;
        }
        return is_normal_ram(md);
}

static __init void reserve_regions(void)
{
...
                if (is_normal_ram(md))
                        early_init_dt_add_memory_arch(paddr, size);

                if (is_reserve_region(md)) {
                        memblock_reserve(paddr, size);
...

static bool __init efi_virtmap_init(void)
{
...
                if (!is_normal_ram(md))
                        prot = __pgprot(PROT_DEVICE_nGnRE);
                else if (md->type == EFI_RUNTIME_SERVICES_CODE ||
                         !PAGE_ALIGNED(md->phys_addr))
                        prot = PAGE_KERNEL_EXEC;
                else
                        prot = PAGE_KERNEL;

Concerns include:

1. is_normal_ram() will see the WB bit and return 1 regardless
of the type.  That seems similar to the arm EFI boot stub issue.
The three callers are shown above.

2. is_reserve_region() treating EFI_PERSISTENT_MEMORY the same
as EFI_CONVENTIONAL_MEMORY looks wrong.

3. We're contemplating working around the grub problem by
reporting EFI_RESERVED_MEMORY plus the NV attribute rather
than EFI_PERSISTENT_MEMORY.

If this is done, then is_reserve_region() will fall through
to is_normal_ram(), which will see the WB bit and return 1.
That seems backwards... but seems correct for persistent
memory, reporting it as a reserved region.  That might avoid the
the EFI_PERSISTENT_MEMORY handling problem (if the preceding
call to is_normal_ram() didn't already cause problems).

---
Robert Elliott, HPE Persistent Memory


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/