Re: [PATCH] x86/traps: Enable UBSAN traps on x86

[Marco Elver]

On Wed, 29 May 2024 at 04:20, Gatlin Newhouse <gatlin.newhouse@xxxxxxxxx> wrote:
[...]
>         if (regs->flags & X86_EFLAGS_IF)
>                 raw_local_irq_enable();
> -       if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
> -           handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
> -               regs->ip += LEN_UD2;
> -               handled = true;
> +
> +       if (insn == INSN_UD2) {
> +               if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
> +               handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
> +                       regs->ip += LEN_UD2;
> +                       handled = true;
> +               }
> +       } else {
> +               if (handle_ubsan_failure(regs, insn) == BUG_TRAP_TYPE_WARN) {

handle_ubsan_failure currently only returns BUG_TRAP_TYPE_NONE?

> +                       if (insn == INSN_REX)
> +                               regs->ip += LEN_REX;
> +                       regs->ip += LEN_UD1;
> +                       handled = true;
> +               }
>         }
>         if (regs->flags & X86_EFLAGS_IF)
>                 raw_local_irq_disable();
> diff --git a/arch/x86/kernel/ubsan.c b/arch/x86/kernel/ubsan.c
> new file mode 100644
> index 000000000000..6cae11f4fe23
> --- /dev/null
> +++ b/arch/x86/kernel/ubsan.c
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Clang Undefined Behavior Sanitizer trap mode support.
> + */
> +#include <linux/bug.h>
> +#include <linux/string.h>
> +#include <linux/printk.h>
> +#include <linux/ubsan.h>
> +#include <asm/ptrace.h>
> +#include <asm/ubsan.h>
> +
> +/*
> + * Checks for the information embedded in the UD1 trap instruction
> + * for the UB Sanitizer in order to pass along debugging output.
> + */
> +enum bug_trap_type handle_ubsan_failure(struct pt_regs *regs, int insn)
> +{
> +       u32 type = 0;
> +
> +       if (insn == INSN_REX) {
> +               type = (*(u16 *)(regs->ip + LEN_REX + LEN_UD1));
> +               if ((type & 0xFF) == 0x40)
> +                       type = (type >> 8) & 0xFF;
> +       } else {
> +               type = (*(u16 *)(regs->ip + LEN_UD1));
> +               if ((type & 0xFF) == 0x40)
> +                       type = (type >> 8) & 0xFF;
> +       }
> +       pr_crit("%s at %pS\n", report_ubsan_failure(regs, type), (void *)regs->ip);
> +
> +       return BUG_TRAP_TYPE_NONE;
> +}

Shouldn't this return BUG_TRAP_TYPE_WARN?