Messages in this thread Patch in this message | | | From | "Kirill A. Shutemov" <> | Subject | [PATCHv3 3/3] x86/tdx: Handle load_unaligned_zeropad() page-cross to a shared page | Date | Wed, 25 May 2022 01:10:12 +0300 |
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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 unwanted loads.
In TDX guests, the second page can be shared page and VMM may configure it to trigger #VE.
Kernel assumes that #VE on a shared page is 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 unaligned MMIO accesses (it includes page-crossings) and fail them. load_unaligned_zeropad() will recover using exception fixups.
The issue was discovered by analysis. It was not triggered during the testing.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/coco/tdx/tdx.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index 94e447e7f103..4e566ed67db8 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -331,6 +331,17 @@ static int handle_mmio(struct pt_regs *regs, struct ve_info *ve) return -EINVAL; } + /* + * MMIO accesses suppose to be naturally aligned and therefore never + * cross a page boundary. Seeing unaligned accesses indicates a bug or + * load_unaligned_zeropad() that steps into unmapped shared page. + * + * In both cases fail the #VE handling. load_unaligned_zeropad() will + * recover using exception fixups. + */ + if ((unsigned long)insn_get_addr_ref(&insn, regs) % size) + return -EFAULT; + /* Handle writes first */ switch (mmio) { case MMIO_WRITE: -- 2.35.1
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