linux-kernel - [PATCH 5.8 042/148] drm/amd/display: fix pow() crashing when given base 0

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Message-Id: <20200824082416.069469455@linuxfoundation.org>
Date:   Mon, 24 Aug 2020 10:29:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Krunoslav Kovac <Krunoslav.Kovac@....com>,
        Anthony Koo <Anthony.Koo@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>
Subject: [PATCH 5.8 042/148] drm/amd/display: fix pow() crashing when given base 0

From: Krunoslav Kovac <Krunoslav.Kovac@....com>

commit d2e59d0ff4c44d1f6f8ed884a5bea7d1bb7fd98c upstream.

[Why&How]
pow(a,x) is implemented as exp(x*log(a)). log(0) will crash.
So return 0^x = 0, unless x=0, convention seems to be 0^0 = 1.

Cc: stable@...r.kernel.org
Signed-off-by: Krunoslav Kovac <Krunoslav.Kovac@....com>
Reviewed-by: Anthony Koo <Anthony.Koo@....com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/amd/display/include/fixed31_32.h |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/gpu/drm/amd/display/include/fixed31_32.h
+++ b/drivers/gpu/drm/amd/display/include/fixed31_32.h
@@ -431,6 +431,9 @@ struct fixed31_32 dc_fixpt_log(struct fi
  */
 static inline struct fixed31_32 dc_fixpt_pow(struct fixed31_32 arg1, struct fixed31_32 arg2)
 {
+	if (arg1.value == 0)
+		return arg2.value == 0 ? dc_fixpt_one : dc_fixpt_zero;
+
 	return dc_fixpt_exp(
 		dc_fixpt_mul(
 			dc_fixpt_log(arg1),