55 lines
2.3 KiB
Diff
55 lines
2.3 KiB
Diff
From 056bc582753699901a534e8546f2829f6ae36497 Mon Sep 17 00:00:00 2001
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Message-Id: <056bc582753699901a534e8546f2829f6ae36497.1601675152.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Thu, 16 Dec 2010 14:25:18 +0100
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Subject: [PATCH 226/333] x86: stackprotector: Avoid random pool on rt
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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CPU bringup calls into the random pool to initialize the stack
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canary. During boot that works nicely even on RT as the might sleep
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checks are disabled. During CPU hotplug the might sleep checks
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trigger. Making the locks in random raw is a major PITA, so avoid the
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call on RT is the only sensible solution. This is basically the same
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randomness which we get during boot where the random pool has no
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entropy and we rely on the TSC randomnness.
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Reported-by: Carsten Emde <carsten.emde@osadl.org>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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arch/x86/include/asm/stackprotector.h | 8 +++++++-
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1 file changed, 7 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
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index 9c556ea2eaa7..b136992beb1b 100644
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--- a/arch/x86/include/asm/stackprotector.h
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+++ b/arch/x86/include/asm/stackprotector.h
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@@ -65,7 +65,7 @@
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*/
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static __always_inline void boot_init_stack_canary(void)
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{
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- u64 canary;
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+ u64 uninitialized_var(canary);
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u64 tsc;
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#ifdef CONFIG_X86_64
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@@ -76,8 +76,14 @@ static __always_inline void boot_init_stack_canary(void)
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* of randomness. The TSC only matters for very early init,
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* there it already has some randomness on most systems. Later
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* on during the bootup the random pool has true entropy too.
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+ * For preempt-rt we need to weaken the randomness a bit, as
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+ * we can't call into the random generator from atomic context
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+ * due to locking constraints. We just leave canary
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+ * uninitialized and use the TSC based randomness on top of it.
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*/
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+#ifndef CONFIG_PREEMPT_RT_FULL
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get_random_bytes(&canary, sizeof(canary));
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+#endif
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tsc = rdtsc();
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canary += tsc + (tsc << 32UL);
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canary &= CANARY_MASK;
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--
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2.17.1
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