On Thu, Jul 11, 2019 at 02:47:51PM -0700, Sean Christopherson wrote:
> 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.
I think this is better and good use of the boolean return value i.e.
consolidate the decision to a single place.
>
> 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
>
Acked-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
/Jarkko
