Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.12 021/110] perf/x86/intel/lbr: Zero the xstate buffer on allocation
Date:   Mon, 28 Jun 2021 10:16:59 -0400
Message-Id: <20210628141828.31757-22-sashal@kernel.org>
In-Reply-To: <20210628141828.31757-1-sashal@kernel.org>
References: <20210628141828.31757-1-sashal@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Thomas Gleixner <tglx@linutronix.de>

[ 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@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/87wnr0wo2z.ffs@nanos.tec.linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/events/intel/lbr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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));
 	}
 }
-- 
2.30.2