Commit 3f8fd02b authored Jul 19, 2019 by Joerg Roedel Committed by Thomas Gleixner Jul 22, 2019

mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()

On x86-32 with PTI enabled, parts of the kernel page-tables are not shared
between processes. This can cause mappings in the vmalloc/ioremap area to
persist in some page-tables after the region is unmapped and released.

When the region is re-used the processes with the old mappings do not fault
in the new mappings but still access the old ones.

This causes undefined behavior, in reality often data corruption, kernel
oopses and panics and even spontaneous reboots.

Fix this problem by activly syncing unmaps in the vmalloc/ioremap area to
all page-tables in the system before the regions can be re-used.

References: https://bugzilla.suse.com/show_bug.cgi?id=1118689

Fixes: 5d72b4fb ('x86, mm: support huge I/O mapping capability I/F')
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20190719184652.11391-4-joro@8bytes.org

parent 8e998fc2

mm/vmalloc.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -1258,6 +1258,12 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
		if (unlikely(valist == NULL))
		return false;

		/*
		* First make sure the mappings are removed from all page-tables
		* before they are freed.
		*/
		vmalloc_sync_all();

		/*
		* TODO: to calculate a flush range without looping.
		* The list can be up to lazy_max_pages() elements.
		@@ -3038,6 +3044,9 @@ EXPORT_SYMBOL(remap_vmalloc_range);
		/*
		* Implement a stub for vmalloc_sync_all() if the architecture chose not to
		* have one.
		*
		* The purpose of this function is to make sure the vmalloc area
		* mappings are identical in all page-tables in the system.
		*/
		void __weak vmalloc_sync_all(void)
		{

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