x86/tdx: Handle load_unaligned_zeropad() page-cross to a shared page
load_unaligned_zeropad() can lead to unwanted loads across page boundaries.
The unwanted loads are typically harmless. But, they might be made to
totally unrelated or even unmapped memory. load_unaligned_zeropad()
relies on exception fixup (#PF, #GP and now #VE) to recover from these
In TDX guests, the second page can be shared page and a VMM may configure
it to trigger #VE.
The kernel assumes that #VE on a shared page is an MMIO access and tries to
decode instruction to handle it. In case of load_unaligned_zeropad() it
may result in confusion as it is not MMIO access.
Fix it by detecting split page MMIO accesses and failing them.
load_unaligned_zeropad() will recover using exception fixups.
The issue was discovered by analysis and reproduced artificially. It was
not triggered during testing.
[ dhansen: fix up changelogs and comments for grammar and clarity,
plus incorporate Kirill's off-by-one fix]
Signed-off-by: Kirill A. Shutemov <email@example.com>
Signed-off-by: Dave Hansen <firstname.lastname@example.org>
1 file changed