[DTrace-devel] [PATCH 2/2] Forbid increasing iregs above default

[Kris Van Hees]

On Thu, Mar 09, 2023 at 11:51:54AM -0500, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> If iregs is set larger than the default, code is generated using
> nonexistent registers and the BPF verifier emits confusing errors.
> 
> Simply do not allow users to increase iregs beyond the default.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>

Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>

> ---
>  libdtrace/dt_options.c            |  2 +-
>  test/unittest/options/err.iregs.d | 16 ++++++++++++++++
>  test/unittest/options/err.iregs.r |  2 ++
>  3 files changed, 19 insertions(+), 1 deletion(-)
>  create mode 100644 test/unittest/options/err.iregs.d
>  create mode 100644 test/unittest/options/err.iregs.r
> 
> diff --git a/libdtrace/dt_options.c b/libdtrace/dt_options.c
> index 1c32dc3d..d25b2ac9 100644
> --- a/libdtrace/dt_options.c
> +++ b/libdtrace/dt_options.c
> @@ -264,7 +264,7 @@ dt_opt_iregs(dtrace_hdl_t *dtp, const char *arg, uintptr_t option)
>  {
>  	int n;
>  
> -	if (arg == NULL || (n = atoi(arg)) <= 0)
> +	if (arg == NULL || (n = atoi(arg)) <= 0 || n > DIF_DIR_NREGS)
>  		return dt_set_errno(dtp, EDT_BADOPTVAL);
>  
>  	dtp->dt_conf.dtc_difintregs = n;
> diff --git a/test/unittest/options/err.iregs.d b/test/unittest/options/err.iregs.d
> new file mode 100644
> index 00000000..ace21d6d
> --- /dev/null
> +++ b/test/unittest/options/err.iregs.d
> @@ -0,0 +1,16 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/* DTrace should recognize when iregs is too great for # of BPF registers */
> +#pragma D option iregs=9
> +
> +BEGIN
> +{
> +	a = 1;
> +	trace(a);
> +	exit(0);
> +}
> diff --git a/test/unittest/options/err.iregs.r b/test/unittest/options/err.iregs.r
> new file mode 100644
> index 00000000..536c3eb8
> --- /dev/null
> +++ b/test/unittest/options/err.iregs.r
> @@ -0,0 +1,2 @@
> +-- @@stderr --
> +dtrace: failed to compile script test/unittest/options/err.iregs.d: line 9: failed to set option 'iregs' to '9': Invalid value for specified option
> -- 
> 2.18.4
> 
> 
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