This is a note to let you know that I've just added the patch titled
perf/x86/intel/lbr: Zero the xstate buffer on allocation
to the 5.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-x86-intel-lbr-zero-the-xstate-buffer-on-allocat.patch
and it can be found in the queue-5.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a93e366bb5cfbd583df26297563d6256d7f6c32d
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Fri Jun 11 15:03:16 2021 +0200
perf/x86/intel/lbr: Zero the xstate buffer on allocation
[ Upstream commit 7f049fbdd57f6ea71dc741d903c19c73b2f70950 ]
XRSTORS requires a valid xstate buffer to work correctly. XSAVES does not
guarantee to write a fully valid buffer according to the SDM:
"XSAVES does not write to any parts of the XSAVE header other than the
XSTATE_BV and XCOMP_BV fields."
XRSTORS triggers a #GP:
"If bytes 63:16 of the XSAVE header are not all zero."
It's dubious at best how this can work at all when the buffer is not zeroed
before use.
Allocate the buffers with __GFP_ZERO to prevent XRSTORS failure.
Fixes: ce711ea3cab9 ("perf/x86/intel/lbr: Support XSAVES/XRSTORS for LBR context switch")
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/87wnr0wo2z.ffs@xxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 22d0e40a1920..991715886246 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -730,7 +730,8 @@ void reserve_lbr_buffers(void)
if (!kmem_cache || cpuc->lbr_xsave)
continue;
- cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache, GFP_KERNEL,
+ cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache,
+ GFP_KERNEL | __GFP_ZERO,
cpu_to_node(cpu));
}
}
