lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 11 Oct 2023 13:43:40 +1000
From: Nicholas Piggin <>
Cc: Nicholas Piggin <>,,
	Pravin B Shelar <>,
	Aaron Conole <>,
	"Eelco Chaudron" <>,
	"Ilya Maximets" <>,
	"Flavio Leitner" <>,
	Ilya Maximets <>
Subject: [PATCH 3/7] openvswitch: reduce stack usage in do_execute_actions

From: Ilya Maximets <>

do_execute_actions() function can be called recursively multiple
times while executing actions that require pipeline forking or
recirculations.  It may also be re-entered multiple times if the packet
leaves openvswitch module and re-enters it through a different port.

Currently, there is a 256-byte array allocated on stack in this
function that is supposed to hold NSH header.  Compilers tend to
pre-allocate that space right at the beginning of the function:

     a88:       48 81 ec b0 01 00 00    sub    $0x1b0,%rsp

NSH is not a very common protocol, but the space is allocated on every
recursive call or re-entry multiplying the wasted stack space.

Move the stack allocation to push_nsh() function that is only used
if NSH actions are actually present.  push_nsh() is also a simple
function without a possibility for re-entry, so the stack is returned
right away.

With this change the preallocated space is reduced by 256 B per call:

     b18:       48 81 ec b0 00 00 00    sub    $0xb0,%rsp

Signed-off-by: Ilya Maximets <>
 net/openvswitch/actions.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 7a66574672d3..be15ef693284 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -349,11 +349,18 @@ static int push_eth(struct sk_buff *skb, struct sw_flow_key *key,
 	return 0;
-static int push_nsh(struct sk_buff *skb, struct sw_flow_key *key,
-		    const struct nshhdr *nh)
+static noinline_for_stack int push_nsh(struct sk_buff *skb,
+				       struct sw_flow_key *key,
+				       const struct nlattr *a)
+	u8 buffer[NSH_HDR_MAX_LEN];
+	struct nshhdr *nh = (struct nshhdr *)buffer;
 	int err;
+	err = nsh_hdr_from_nlattr(a, nh, NSH_HDR_MAX_LEN);
+	if (err)
+		return err;
 	err = nsh_push(skb, nh);
 	if (err)
 		return err;
@@ -1477,17 +1484,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			err = pop_eth(skb, key);
-			u8 buffer[NSH_HDR_MAX_LEN];
-			struct nshhdr *nh = (struct nshhdr *)buffer;
-			err = nsh_hdr_from_nlattr(nla_data(a), nh,
-						  NSH_HDR_MAX_LEN);
-			if (unlikely(err))
-				break;
-			err = push_nsh(skb, key, nh);
+			err = push_nsh(skb, key, nla_data(a));
-		}
 			err = pop_nsh(skb, key);

Powered by blists - more mailing lists