In generic_load_microcode(), curr_mc_size is the size of the last
allocated buffer and since we have this performance "optimization"
there to vmalloc a new buffer only when the current one is bigger,
curr_mc_size ends up becoming the size of the biggest buffer we've seen
so far.
However, we end up saving the microcode patch which matches our CPU
and its size is not curr_mc_size but the respective mc_size during the
iteration while we're staring at it.
So save that mc_size into a separate variable and use it to store the
previously found microcode buffer.
Without this fix, we could get oops like this:
BUG: unable to handle kernel paging request at ffffc9000e30f000
IP: __memcpy+0x12/0x20
...
Call Trace:
? kmemdup+0x43/0x60
__alloc_microcode_buf+0x44/0x70
save_microcode_patch+0xd4/0x150
generic_load_microcode+0x1b8/0x260
request_microcode_user+0x15/0x20
microcode_write+0x91/0x100
__vfs_write+0x34/0x120
vfs_write+0xc1/0x130
SyS_write+0x56/0xc0
do_syscall_64+0x6c/0x160
entry_SYSCALL64_slow_path+0x25/0x25
Fixes: 06b8534cb7 ("x86/microcode: Rework microcode loading")
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/4f33cbfd-44f2-9bed-3b66-7446cd14256f@ce.jp.nec.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2e86222c67