The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: ceba767b943de2128eaef95e19880809274ac35d
Gitweb: https://git.kernel.org/tip/ceba767b943de2128eaef95e19880809274ac35d
Author: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
AuthorDate: Tue, 14 Jun 2022 15:01:35 +03:00
Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Fri, 17 Jun 2022 14:30:20 -07:00
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@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20220614120135.14812-4-kirill.shutemov@xxxxxxxxxxxxxxx
---
arch/x86/coco/tdx/tdx.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index c8d44f4..d5c51c9 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) / PAGE_SIZE)
+ return -EFAULT;
+
/* Handle writes first */
switch (mmio) {
case MMIO_WRITE:
|