From 36515185fa3c1227810c1c6a21f07a5353c3658e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 16 Dec 2010 14:25:18 +0100 Subject: [PATCH 109/166] x86: stackprotector: Avoid random pool on rt CPU bringup calls into the random pool to initialize the stack canary. During boot that works nicely even on RT as the might sleep checks are disabled. During CPU hotplug the might sleep checks trigger. Making the locks in random raw is a major PITA, so avoid the call on RT is the only sensible solution. This is basically the same randomness which we get during boot where the random pool has no entropy and we rely on the TSC randomnness. Reported-by: Carsten Emde Signed-off-by: Thomas Gleixner --- arch/x86/include/asm/stackprotector.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) Index: linux-5.15.32-rt39/arch/x86/include/asm/stackprotector.h =================================================================== --- linux-5.15.32-rt39.orig/arch/x86/include/asm/stackprotector.h +++ linux-5.15.32-rt39/arch/x86/include/asm/stackprotector.h @@ -50,7 +50,7 @@ */ static __always_inline void boot_init_stack_canary(void) { - u64 canary; + u64 canary = 0; u64 tsc; #ifdef CONFIG_X86_64 @@ -61,8 +61,14 @@ static __always_inline void boot_init_st * of randomness. The TSC only matters for very early init, * there it already has some randomness on most systems. Later * on during the bootup the random pool has true entropy too. + * For preempt-rt we need to weaken the randomness a bit, as + * we can't call into the random generator from atomic context + * due to locking constraints. We just leave canary + * uninitialized and use the TSC based randomness on top of it. */ +#ifndef CONFIG_PREEMPT_RT get_random_bytes(&canary, sizeof(canary)); +#endif tsc = rdtsc(); canary += tsc + (tsc << 32UL); canary &= CANARY_MASK;