This is a note to let you know that I've just added the patch titled

x86/microcode: Fix again accessing initrd after having been freed

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-microcode-fix-again-accessing-initrd-after-having-been-freed.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 1d080f096fe33f031d26e19b3ef0146f66b8b0f1 Mon Sep 17 00:00:00 2001

From: Borislav Petkov bp@suse.de Date: Tue, 23 Jan 2018 11:41:33 +0100 Subject: x86/microcode: Fix again accessing initrd after having been freed

From: Borislav Petkov bp@suse.de

commit 1d080f096fe33f031d26e19b3ef0146f66b8b0f1 upstream.

Commit 24c2503255d3 ("x86/microcode: Do not access the initrd after it has been freed") fixed attempts to access initrd from the microcode loader after it has been freed. However, a similar KASAN warning was reported (stack trace edited):

smpboot: Booting Node 0 Processor 1 APIC 0x11 ================================================================== BUG: KASAN: use-after-free in find_cpio_data+0x9b5/0xa50 Read of size 1 at addr ffff880035ffd000 by task swapper/1/0

CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.14.8-slack #7 Hardware name: System manufacturer System Product Name/A88X-PLUS, BIOS 3003 03/10/2016 Call Trace: dump_stack print_address_description kasan_report ? find_cpio_data __asan_report_load1_noabort find_cpio_data find_microcode_in_initrd __load_ucode_amd load_ucode_amd_ap load_ucode_ap

After some investigation, it turned out that a merge was done using the wrong side to resolve, leading to picking up the previous state, before the 24c2503255d3 fix. Therefore the Fixes tag below contains a merge commit.

Revert the mismerge by catching the save_microcode_in_initrd_amd() retval and thus letting the function exit with the last return statement so that initrd_gone can be set to true.

Fixes: f26483eaedec ("Merge branch 'x86/urgent' into x86/microcode, to resolve conflicts") Reported-by: higuita@gmx.net Signed-off-by: Borislav Petkov bp@suse.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://bugzilla.kernel.org/show_bug.cgi?id=198295 Link: https://lkml.kernel.org/r/20180123104133.918-2-bp@alien8.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/kernel/cpu/microcode/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -239,7 +239,7 @@ static int __init save_microcode_in_init break; case X86_VENDOR_AMD: if (c->x86 >= 0x10) - return save_microcode_in_initrd_amd(cpuid_eax(1)); + ret = save_microcode_in_initrd_amd(cpuid_eax(1)); break; default: break;

Patches currently in stable-queue which might be from bp@suse.de are

queue-4.14/x86-microcode-intel-extend-bdw-late-loading-further-with-llc-size-check.patch queue-4.14/x86-microcode-fix-again-accessing-initrd-after-having-been-freed.patch