linux-kernel - [PATCH v2] drm/i915: Fix possible int overflow in skl_ddi_calculate

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Message-ID: <20240729174035.25727-1-n.zhandarovich@fintech.ru>
Date: Mon, 29 Jul 2024 10:40:35 -0700
From: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To: Jani Nikula <jani.nikula@...ux.intel.com>, Rodrigo Vivi
	<rodrigo.vivi@...el.com>, Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
CC: Nikita Zhandarovich <n.zhandarovich@...tech.ru>, Tvrtko Ursulin
	<tursulin@...ulin.net>, David Airlie <airlied@...il.com>, Daniel Vetter
	<daniel@...ll.ch>, Ville Syrjälä
	<ville.syrjala@...ux.intel.com>, <intel-gfx@...ts.freedesktop.org>,
	<intel-xe@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>,
	<stable@...r.kernel.org>
Subject: [PATCH v2] drm/i915: Fix possible int overflow in skl_ddi_calculate_wrpll()

On the off chance that clock value ends up being too high (by means
of skl_ddi_calculate_wrpll() having benn called with big enough
value of crtc_state->port_clock * 1000), one possible consequence
may be that the result will not be able to fit into signed int.

Fix this issue by moving conversion of clock parameter from kHz to Hz
into the body of skl_ddi_calculate_wrpll(), as well as casting the
same parameter to u64 type while calculating the value for AFE clock.
This both mitigates the overflow problem and avoids possible erroneous
integer promotion mishaps.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: fe70b262e781 ("drm/i915: Move a bunch of stuff into rodata from the stack")
Cc: stable@...r.kernel.org
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
---
v2: instead of double casting of 'clock' with (u64)(u32), convert
'clock' to Hz inside skl_ddi_calculate_wrpll() and cast it only
to u64 to mitigate the issue. Per Jani's <jani.nikula@...ux.intel.com>
helpful suggestion made here:
https://lore.kernel.org/all/87ed7gzhin.fsf@intel.com/
Also, change commit description accordingly.

v1: https://lore.kernel.org/all/20240724184911.12250-1-n.zhandarovich@fintech.ru/

 drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
index 90998b037349..292d163036b1 100644
--- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
@@ -1658,7 +1658,7 @@ static void skl_wrpll_params_populate(struct skl_wrpll_params *params,
 }
 
 static int
-skl_ddi_calculate_wrpll(int clock /* in Hz */,
+skl_ddi_calculate_wrpll(int clock,
 			int ref_clock,
 			struct skl_wrpll_params *wrpll_params)
 {
@@ -1683,7 +1683,7 @@ skl_ddi_calculate_wrpll(int clock /* in Hz */,
 	};
 	unsigned int dco, d, i;
 	unsigned int p0, p1, p2;
-	u64 afe_clock = clock * 5; /* AFE Clock is 5x Pixel clock */
+	u64 afe_clock = (u64)clock * 1000 * 5; /* AFE Clock is 5x Pixel clock, in Hz */
 
 	for (d = 0; d < ARRAY_SIZE(dividers); d++) {
 		for (dco = 0; dco < ARRAY_SIZE(dco_central_freq); dco++) {
@@ -1808,7 +1808,7 @@ static int skl_ddi_hdmi_pll_dividers(struct intel_crtc_state *crtc_state)
 	struct skl_wrpll_params wrpll_params = {};
 	int ret;
 
-	ret = skl_ddi_calculate_wrpll(crtc_state->port_clock * 1000,
+	ret = skl_ddi_calculate_wrpll(crtc_state->port_clock,
 				      i915->display.dpll.ref_clks.nssc, &wrpll_params);
 	if (ret)
 		return ret;