Commit 2cb15faa authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
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x86/cpu: Re-enable stackprotector 



Commit 5416c266 ("x86: make sure load_percpu_segment has no
stackprotector") disabled the stackprotector for cpu/common.c because of
load_percpu_segment(). Back then the boot stack canary was initialized very
early in start_kernel(). Switching the per CPU area by loading the GDT
caused the stackprotector to fail with paravirt enabled kernels as the
GSBASE was not updated yet. In hindsight a wrong change because it would
have been sufficient to ensure that the canary is the same in both per CPU
areas.

Commit d5553523 ("random: move rand_initialize() earlier") moved the
stack canary initialization to a later point in the init sequence. As a
consequence the per CPU stack canary is 0 when switching the per CPU areas,
so there is no requirement anymore to exclude this file.

Add a comment to load_percpu_segment().

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111143.303010511@infradead.org
parent 1f19e2d5

arch/x86/kernel/cpu/Makefile

+0 −3
Original line number Diff line number Diff line
@@ -17,9 +17,6 @@ KMSAN_SANITIZE_common.o := n 
# As above, instrumenting secondary CPU boot code causes boot hangs.

KCSAN_SANITIZE_common.o := n



# Make sure load_percpu_segment has no stackprotector

CFLAGS_common.o		:= -fno-stack-protector



obj-y			:= cacheinfo.o scattered.o topology.o

obj-y			+= common.o

obj-y			+= rdrand.o

arch/x86/kernel/cpu/common.c

+3 −0
Original line number Diff line number Diff line
@@ -752,6 +752,9 @@ void __init switch_gdt_and_percpu_base(int cpu) 
	 * early mapping is still valid. That means the GSBASE update will

	 * lose any prior per CPU data which was not copied over in

	 * setup_per_cpu_areas().

	 *

	 * This works even with stackprotector enabled because the

	 * per CPU stack canary is 0 in both per CPU areas.

	 */

	wrmsrl(MSR_GS_BASE, cpu_kernelmode_gs_base(cpu));

#else