Re: [PATCH] x86/mm: determine whether the fault address is canonical

From: Andy Lutomirski
Date: Fri Oct 04 2019 - 10:59:16 EST


On Fri, Oct 4, 2019 at 6:45 AM Changbin Du <changbin.du@xxxxxxxxx> wrote:
>
> We know the answer, so don't ask the user.
>
> Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
> ---
> arch/x86/mm/extable.c | 5 ++++-
> arch/x86/mm/mm_internal.h | 11 +++++++++++
> 2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
> index 4d75bc656f97..5196e586756f 100644
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -8,6 +8,8 @@
> #include <asm/traps.h>
> #include <asm/kdebug.h>
>
> +#include "mm_internal.h"
> +
> typedef bool (*ex_handler_t)(const struct exception_table_entry *,
> struct pt_regs *, int, unsigned long,
> unsigned long);
> @@ -123,7 +125,8 @@ __visible bool ex_handler_uaccess(const struct exception_table_entry *fixup,
> unsigned long error_code,
> unsigned long fault_addr)
> {
> - WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. Non-canonical address?");
> + WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault at %s address in user access.",
> + is_canonical_addr(fault_addr) ? "canonical" : "non-canonical");

Unless the hardware behaves rather differently from the way I think it
does, fault_addr is garbage for anything other than #PF and sometimes
for #DF. (And maybe the virtualization faults?) I don't believe that
#GP fills in CR2.