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Message-Id: <20220517153021.11116-1-kirill.shutemov@linux.intel.com>
Date: Tue, 17 May 2022 18:30:21 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...el.com, luto@...nel.org, peterz@...radead.org
Cc: sathyanarayanan.kuppuswamy@...ux.intel.com, ak@...ux.intel.com,
dan.j.williams@...el.com, david@...hat.com, hpa@...or.com,
seanjc@...gle.com, thomas.lendacky@....com, x86@...nel.org,
linux-kernel@...r.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] 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
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@...ux.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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