[PATCH 6.1 555/609] net: octeontx2-pf: Fix UB in shift operation

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sergey V. Frolov <[email protected]>

commit 7e2d693af0d4c05bddccb3541a0aabd69f4cb244 upstream.

In function otx2_get_egress_burst_cfg, when the parameter `burst` is
255 and the max mantissa is 255 (0xFFULL), `burst_exp` is set to
`ilog2(255) - 1`, which equals 6.

This results in an unsigned wrap-around when calculating
`(1ULL << (*burst_exp - 7))`, since `*burst_exp - 7` becomes -1,
which makes the shift operand 0xFFFFFFFF. This value is greater than
the width of the left operand.

According to standard 6.5.7 p.3:
"The type of the result is that of the promoted left operand.
If the value of the right operand is negative or is greater than
or equal to the width of the promoted left operand, the behavior
is undefined."

Fix the off-by-one boundary condition.

Add a WARN_ON(*burst_exp < 7) before the else branch as an
explicit safeguard. This ensures that if max_mantissa ever changes
in a way that reintroduces this condition, it will be immediately
caught at runtime rather than silently triggering UB.

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

Fixes: e638a83f167e ("octeontx2-pf: TC_MATCHALL egress ratelimiting offload")
Signed-off-by: Sergey V. Frolov <[email protected]>
Cc: [email protected]
Reviewed-by: Ratheesh Kannoth <[email protected]>
Reviewed-by: Sunil Goutham <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c
+++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c
@@ -86,10 +86,12 @@ static void otx2_get_egress_burst_cfg(st
 	if (burst) {
 		*burst_exp = ilog2(burst) ? ilog2(burst) - 1 : 0;
 		tmp = burst - rounddown_pow_of_two(burst);
-		if (burst < max_mantissa)
+		if (burst <= max_mantissa) {
 			*burst_mantissa = tmp * 2;
-		else
+		} else {
+			WARN_ON(*burst_exp < 7);
 			*burst_mantissa = tmp / (1ULL << (*burst_exp - 7));
+		}
 	} else {
 		*burst_exp = MAX_BURST_EXPONENT;
 		*burst_mantissa = max_mantissa;