Messages in this thread Patch in this message | | | From | "Kirill A. Shutemov" <> | Subject | [PATCH] x86/tdx: Handle load_unaligned_zeropad() page-cross to a shared page | Date | Tue, 17 May 2022 18:30:21 +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 guest 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.
Check fixup table before trying to handle MMIO.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/coco/tdx/tdx.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index 03deb4d6920d..5fbdda2f2b86 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -11,6 +11,8 @@ #include <asm/insn.h> #include <asm/insn-eval.h> #include <asm/pgtable.h> +#include <asm/trapnr.h> +#include <asm/extable.h> /* TDX module Call Leaf IDs */ #define TDX_GET_INFO 1 @@ -296,6 +298,26 @@ static bool handle_mmio(struct pt_regs *regs, struct ve_info *ve) if (WARN_ON_ONCE(user_mode(regs))) return false; + /* + * load_unaligned_zeropad() relies on exception fixups in case of the + * word being a page-crosser and the second page is not accessible. + * + * In TDX guest 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. + * + * Check fixup table before trying to handle MMIO. + */ + if (fixup_exception(regs, X86_TRAP_VE, 0, ve->gla)) { + /* regs->ip is adjusted by fixup_exception() */ + ve->instr_len = 0; + + return true; + } + if (copy_from_kernel_nofault(buffer, (void *)regs->ip, MAX_INSN_SIZE)) return false; -- 2.35.1
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