From: Thomas Gleixner Date: Thu, 15 Sep 2022 11:10:43 +0000 (+0200) Subject: x86/cpu: Re-enable stackprotector X-Git-Tag: v6.6.17~5918^2~79 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=2cb15faaedeb67f52f2ddc32b5ca152acfc422c2;p=platform%2Fkernel%2Flinux-rpi.git x86/cpu: Re-enable stackprotector Commit 5416c2663517 ("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 d55535232c3d ("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: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220915111143.303010511@infradead.org --- diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile index f10a921..d7e3cea 100644 --- a/arch/x86/kernel/cpu/Makefile +++ b/arch/x86/kernel/cpu/Makefile @@ -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 diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index f51928d..8e87318 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -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