[PATCH v5 02/10] x86/boot: Allow a "silent" kaslr random byte fetch

[Kristen Carlson Accardi]

From: Kees Cook <keesc...@chromium.org>

Under earlyprintk, each RNG call produces a debug report line. When
shuffling hundreds of functions, this is not useful information (each
line is identical and tells us nothing new). Instead, allow for a NULL
"purpose" to suppress the debug reporting.

Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: Kristen Carlson Accardi <kris...@linux.intel.com>
---
 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;
 }
-- 
2.20.1