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kexec: introduce sysctl parameters kexec_load_limit_*

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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 <ribalda@chromium.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Ross Zwisler <zwisler@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ricardo Ribalda
2023-01-04 15:38:48 +01:00
committed by Andrew Morton
parent 7e99f8b69c
commit a42aaad2e4
5 changed files with 114 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
kernel/kexec_file.c
View File

@@ -326,11 +326,13 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
unsigned long, cmdline_len, const char __user *, cmdline_ptr,
unsigned long, flags)
{
int ret = 0, i;
int image_type = (flags & KEXEC_FILE_ON_CRASH) ?
KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT;
struct kimage **dest_image, *image;
int ret = 0, i;
/* We only trust the superuser with rebooting the system. */
if (!kexec_load_permitted())
if (!kexec_load_permitted(image_type))
return -EPERM;
/* Make sure we have a legal set of flags */
@@ -342,11 +344,12 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
if (!kexec_trylock())
return -EBUSY;
dest_image = &kexec_image;
if (flags & KEXEC_FILE_ON_CRASH) {
if (image_type == KEXEC_TYPE_CRASH) {
dest_image = &kexec_crash_image;
if (kexec_crash_image)
arch_kexec_unprotect_crashkres();
} else {
dest_image = &kexec_image;
}
if (flags & KEXEC_FILE_UNLOAD)