6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: David Woodhouse <dwmw@xxxxxxxxxxxx>
commit 07fa619f2a40c221ea27747a3323cabc59ab25eb upstream.
The restore_processor_state() function explicitly states that "the asm code
that gets us here will have restored a usable GDT". That wasn't true in the
case of returning from a ::preserve_context kexec. Make it so.
Without this, the kernel was depending on the called function to reload a
GDT which is appropriate for the kernel before returning.
Test program:
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <linux/kexec.h>
#include <linux/reboot.h>
#include <sys/reboot.h>
#include <sys/syscall.h>
int main (void)
{
struct kexec_segment segment = {};
unsigned char purgatory[] = {
0x66, 0xba, 0xf8, 0x03, // mov $0x3f8, %dx
0xb0, 0x42, // mov $0x42, %al
0xee, // outb %al, (%dx)
0xc3, // ret
};
int ret;
segment.buf = &purgatory;
segment.bufsz = sizeof(purgatory);
segment.mem = (void *)0x400000;
segment.memsz = 0x1000;
ret = syscall(__NR_kexec_load, 0x400000, 1, &segment, KEXEC_PRESERVE_CONTEXT);
if (ret) {
perror("kexec_load");
exit(1);
}
ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_KEXEC);
if (ret) {
perror("kexec reboot");
exit(1);
}
printf("Success\n");
return 0;
}
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20241205153343.3275139-2-dwmw2@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/relocate_kernel_64.S | 7 +++++++
1 file changed, 7 insertions(+)
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -242,6 +242,13 @@ SYM_CODE_START_LOCAL_NOALIGN(virtual_map
movq CR0(%r8), %r8
movq %rax, %cr3
movq %r8, %cr0
+
+#ifdef CONFIG_KEXEC_JUMP
+ /* Saved in save_processor_state. */
+ movq $saved_context, %rax
+ lgdt saved_context_gdt_desc(%rax)
+#endif
+
movq %rbp, %rax
popf
