Do not fixup #DB or #BP exceptions that are reported on the SGX vDSO's
ENCLU, as it's impossible to determine whether or not the exception
originated from within an enclave, e.g. a #DB in an enclave will look
identical to a #DB on the ENCLU itself. Even if hardware provided a
magic flag to identify enclave exceptions, #DB still has scenarios where
the intended recipient is ambiguous, e.g. a data breakpoint encountered
in the enclave but on an address outside of the enclave, a breakpoint
encountered in the enclave and a simultaneouls code breakpoint on ENCLU,
and so on and so forth.
An alternative solution would be to simply not call the vDSO fixup
routine for #DB or #BP. Rejecting fixup from within vDSO explicitly
documents that #DB/#BP are intentionally skipped and provides a single
location for determining what exceptions are indeed handled by vDSO
fixup.
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/entry/vdso/extable.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/x86/entry/vdso/extable.c b/arch/x86/entry/vdso/extable.c
index 49284d560d36..afcf5b65beef 100644
--- a/arch/x86/entry/vdso/extable.c
+++ b/arch/x86/entry/vdso/extable.c
@@ -2,6 +2,7 @@
#include <linux/err.h>
#include <linux/mm.h>
#include <asm/current.h>
+#include <asm/traps.h>
#include <asm/vdso.h>
struct vdso_exception_table_entry {
@@ -16,6 +17,14 @@ bool fixup_vdso_exception(struct pt_regs *regs, int trapnr,
unsigned int nr_entries, i;
unsigned long base;
+ /*
+ * Do not attempt to fixup #DB or #BP. It's impossible to identify
+ * whether or not a #DB/#BP originated from within an SGX enclave and
+ * SGX enclaves are currently the only use case for vDSO fixup.
+ */
+ if (trapnr == X86_TRAP_DB || trapnr == X86_TRAP_BP)
+ return false;
+
if (!current->mm->context.vdso)
return false;
--
2.22.0
