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From: "tip-bot2 for Kees Cook" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: x86/core] x86/boot: Allow a "silent" kaslr random byte fetch
Date: Thu, 28 Oct 2021 13:29:34 -0000	[thread overview]
Message-ID: <163542777462.626.1639307537615391982.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20211013175742.1197608-3-keescook@chromium.org>

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     0d054d4e82072bcfd5eb961536b09a9b3f5613fb
Gitweb:        https://git.kernel.org/tip/0d054d4e82072bcfd5eb961536b09a9b3f5613fb
Author:        Kees Cook <keescook@chromium.org>
AuthorDate:    Wed, 13 Oct 2021 10:57:40 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 27 Oct 2021 11:07:58 +02:00

x86/boot: Allow a "silent" kaslr random byte fetch

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.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20211013175742.1197608-3-keescook@chromium.org
---
 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 a536651..2b3eb8c 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;
 }

  parent reply	other threads:[~2021-10-28 13:29 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-13 17:57 [PATCH 0/4] x86: Various clean-ups in support of FGKASLR Kees Cook
2021-10-13 17:57 ` [PATCH 1/4] x86/tools/relocs: Support >64K section headers Kees Cook
2021-10-28 13:29   ` [tip: x86/core] " tip-bot2 for Kristen Carlson Accardi
2021-10-13 17:57 ` [PATCH 2/4] x86/boot: Allow a "silent" kaslr random byte fetch Kees Cook
2021-10-13 18:10   ` Nick Desaulniers
2021-10-28 13:29   ` tip-bot2 for Kees Cook [this message]
2021-10-13 17:57 ` [PATCH 3/4] x86/boot/compressed: Avoid duplicate malloc() implementations Kees Cook
2021-10-28 13:29   ` [tip: x86/core] " tip-bot2 for Kees Cook
2021-10-13 17:57 ` [PATCH 4/4] vmlinux.lds.h: Have ORC lookup cover entire _etext - _stext Kees Cook
2021-10-14  0:29   ` Josh Poimboeuf
2021-10-28 13:29   ` [tip: x86/core] " tip-bot2 for Kristen Carlson Accardi
2021-10-15 18:27 ` [PATCH 0/4] x86: Various clean-ups in support of FGKASLR Alexander Lobakin
2021-10-27  6:10 ` Kees Cook
2021-10-27  6:57 ` Peter Zijlstra

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