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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Nicholas Piggin <npiggin@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Mahesh Salgaonkar <mahesh@linux.ibm.com>,
        Sasha Levin <sashal@kernel.org>, linuxppc-dev@lists.ozlabs.org
Subject: [PATCH AUTOSEL 5.7 220/388] powerpc/pseries/ras: Fix FWNMI_VALID off by one
Date:   Wed, 17 Jun 2020 21:05:17 -0400
Message-Id: <20200618010805.600873-220-sashal@kernel.org>
In-Reply-To: <20200618010805.600873-1-sashal@kernel.org>
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From: Nicholas Piggin <npiggin@gmail.com>

[ Upstream commit deb70f7a35a22dffa55b2c3aac71bc6fb0f486ce ]

This was discovered developing qemu fwnmi sreset support. This
off-by-one bug means the last 16 bytes of the rtas area can not
be used for a 16 byte save area.

It's not a serious bug, and QEMU implementation has to retain a
workaround for old kernels, but it's good to tighten it.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Link: https://lore.kernel.org/r/20200508043408.886394-7-npiggin@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/powerpc/platforms/pseries/ras.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
index 1d1da639b8b7..16ba5c542e55 100644
--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -395,10 +395,11 @@ static irqreturn_t ras_error_interrupt(int irq, void *dev_id)
 /*
  * Some versions of FWNMI place the buffer inside the 4kB page starting at
  * 0x7000. Other versions place it inside the rtas buffer. We check both.
+ * Minimum size of the buffer is 16 bytes.
  */
 #define VALID_FWNMI_BUFFER(A) \
-	((((A) >= 0x7000) && ((A) < 0x7ff0)) || \
-	(((A) >= rtas.base) && ((A) < (rtas.base + rtas.size - 16))))
+	((((A) >= 0x7000) && ((A) <= 0x8000 - 16)) || \
+	(((A) >= rtas.base) && ((A) <= (rtas.base + rtas.size - 16))))
 
 static inline struct rtas_error_log *fwnmi_get_errlog(void)
 {
-- 
2.25.1