On Wed, Oct 13, 2021 at 10:57 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> Under earlyprintk, each RNG call produces a debug report line. To support
> the future FGKASLR feature, which will fetch random bytes during function
> shuffling, this is not useful information (each line is identical and
> tells us nothing new), needlessly spamming the console. Instead, allow
> for a NULL "purpose" to suppress the debug reporting.
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> arch/x86/lib/kaslr.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c
> index a53665116458..2b3eb8c948a3 100644
> --- a/arch/x86/lib/kaslr.c
> +++ b/arch/x86/lib/kaslr.c
> @@ -56,11 +56,14 @@ unsigned long kaslr_get_random_long(const char *purpose)
> unsigned long raw, random = get_boot_seed();
> bool use_i8254 = true;
>
> - debug_putstr(purpose);
> - debug_putstr(" KASLR using");
> + if (purpose) {
> + debug_putstr(purpose);
> + debug_putstr(" KASLR using");
> + }
>
> if (has_cpuflag(X86_FEATURE_RDRAND)) {
> - debug_putstr(" RDRAND");
> + if (purpose)
> + debug_putstr(" RDRAND");
> if (rdrand_long(&raw)) {
> random ^= raw;
> use_i8254 = false;
> @@ -68,7 +71,8 @@ unsigned long kaslr_get_random_long(const char *purpose)
> }
>
> if (has_cpuflag(X86_FEATURE_TSC)) {
> - debug_putstr(" RDTSC");
> + if (purpose)
> + debug_putstr(" RDTSC");
> raw = rdtsc();
>
> random ^= raw;
> @@ -76,7 +80,8 @@ unsigned long kaslr_get_random_long(const char *purpose)
> }
>
> if (use_i8254) {
> - debug_putstr(" i8254");
> + if (purpose)
> + debug_putstr(" i8254");
> random ^= i8254();
> }
>
> @@ -86,7 +91,8 @@ unsigned long kaslr_get_random_long(const char *purpose)
> : "a" (random), "rm" (mix_const));
> random += raw;
>
> - debug_putstr("...\n");
> + if (purpose)
> + debug_putstr("...\n");
>
> return random;
> }
> --
> 2.30.2
>
--
Thanks,
~Nick Desaulniers
