From a42aaad2e47b23d63037bfc0130e33fc0f74cd71 Mon Sep 17 00:00:00 2001 From: Ricardo Ribalda Date: Wed, 4 Jan 2023 15:38:48 +0100 Subject: kexec: introduce sysctl parameters kexec_load_limit_* kexec allows replacing the current kernel with a different one. This is usually a source of concerns for sysadmins that want to harden a system. Linux already provides a way to disable loading new kexec kernel via kexec_load_disabled, but that control is very coard, it is all or nothing and does not make distinction between a panic kexec and a normal kexec. This patch introduces new sysctl parameters, with finer tuning to specify how many times a kexec kernel can be loaded. The sysadmin can set different limits for kexec panic and kexec reboot kernels. The value can be modified at runtime via sysctl, but only with a stricter value. With these new parameters on place, a system with loadpin and verity enabled, using the following kernel parameters: sysctl.kexec_load_limit_reboot=0 sysct.kexec_load_limit_panic=1 can have a good warranty that if initrd tries to load a panic kernel, a malitious user will have small chances to replace that kernel with a different one, even if they can trigger timeouts on the disk where the panic kernel lives. Link: https://lkml.kernel.org/r/20221114-disable-kexec-reset-v6-3-6a8531a09b9a@chromium.org Signed-off-by: Ricardo Ribalda Reviewed-by: Steven Rostedt (Google) Acked-by: Baoquan He Cc: Bagas Sanjaya Cc: "Eric W. Biederman" Cc: Guilherme G. Piccoli # Steam Deck Cc: Joel Fernandes (Google) Cc: Jonathan Corbet Cc: Philipp Rudo Cc: Ross Zwisler Cc: Sergey Senozhatsky Signed-off-by: Andrew Morton --- kernel/kexec.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'kernel/kexec.c') diff --git a/kernel/kexec.c b/kernel/kexec.c index ce1bca874a8d..92d301f98776 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -190,10 +190,12 @@ out_unlock: static inline int kexec_load_check(unsigned long nr_segments, unsigned long flags) { + int image_type = (flags & KEXEC_ON_CRASH) ? + KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT; int result; /* We only trust the superuser with rebooting the system. */ - if (!kexec_load_permitted()) + if (!kexec_load_permitted(image_type)) return -EPERM; /* Permit LSMs and IMA to fail the kexec */ -- cgit v1.2.3-59-g8ed1b