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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2022-06-14 15:01:35 +0300
committerDave Hansen <dave.hansen@linux.intel.com>2022-06-17 15:37:33 -0700
commit1e7769653b06b56b7ea7d56911d2d5b2957750cd (patch)
tree25a3810999acb293a056132330d6c3b872fb850b
parentcdd85786f4b3b9273e4376e69aa95a2d71722764 (diff)
downloadlinux-1e7769653b06b56b7ea7d56911d2d5b2957750cd.tar.bz2
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 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 <kirill.shutemov@linux.intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://lkml.kernel.org/r/20220614120135.14812-4-kirill.shutemov@linux.intel.com
-rw-r--r--arch/x86/coco/tdx/tdx.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index c8d44f463283..928dcf7a20d9 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -333,8 +333,8 @@ static bool mmio_write(int size, unsigned long addr, unsigned long val)
static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
{
+ unsigned long *reg, val, vaddr;
char buffer[MAX_INSN_SIZE];
- unsigned long *reg, val;
struct insn insn = {};
enum mmio_type mmio;
int size, extend_size;
@@ -360,6 +360,19 @@ static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
return -EINVAL;
}
+ /*
+ * Reject EPT violation #VEs that split pages.
+ *
+ * MMIO accesses are supposed to be naturally aligned and therefore
+ * never cross page boundaries. Seeing split page accesses indicates
+ * a bug or a load_unaligned_zeropad() that stepped into an MMIO page.
+ *
+ * load_unaligned_zeropad() will recover using exception fixups.
+ */
+ vaddr = (unsigned long)insn_get_addr_ref(&insn, regs);
+ if (vaddr / PAGE_SIZE != (vaddr + size - 1) / PAGE_SIZE)
+ return -EFAULT;
+
/* Handle writes first */
switch (mmio) {
case MMIO_WRITE: