Messages in this thread | | | Date | Mon, 21 Jul 2014 17:46:34 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH RFC 5/9] ARM: Add L1 PTE non-secure mapping |
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On Mon, Jul 21, 2014 at 03:47:16PM +0100, Daniel Thompson wrote: > From: Marek Vasut <marex@denx.de> > > Add new device type, MT_DEVICE_NS. This type sets the NS bit in L1 PTE [1]. > Accesses to a memory region which is mapped this way generate non-secure > access to that memory area. One must be careful here, since the NS bit is > only available in L1 PTE, therefore when creating the mapping, the mapping > must be at least 1 MiB big and must be aligned to 1 MiB. If that condition > was false, the kernel would use regular L2 page mapping for this area instead > and the NS bit setting would be ineffective.
Right, so this says that PTE mappings are not permissible.
> + [MT_DEVICE_NS] = { /* Non-secure accesses from secure mode */ > + .prot_pte = PROT_PTE_DEVICE | L_PTE_MT_DEV_SHARED | > + L_PTE_SHARED, > + .prot_l1 = PMD_TYPE_TABLE,
However, by filling in prot_pte and prot_l1, you're telling the code that it /can/ setup such a mapping. This is screwed.
If you want to deny anything but section mappings (because they don't work) then you omit prot_pte and prot_l1. With those omitted, if someone tries to abuse this mapping type, then this check in create_mapping() will trigger:
if (type->prot_l1 == 0 && ((addr | phys | length) & ~SECTION_MASK)) { printk(KERN_WARNING "BUG: map for 0x%08llx at 0x%08lx can not " "be mapped using pages, ignoring.\n", (long long)__pfn_to_phys(md->pfn), addr); return; }
ioremap doesn't have that check; it assumes that it will always be setting up PTE mappings via ioremap_page_range(). In fact, on many platforms that's the only option.
So making this interface available via ioremap() seems pointless - but more importantly it's extremely error-prone. So, MT_DEVICE_NS shouldn't be using 4 at all, shouldn't be in asm/io.h, but should be with the private MT_* definitions in map.h.
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