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From: Stefano Brivio <sbrivio@redhat.com>
To: passt-dev@passt.top
Subject: [PATCH] pasta, util: Align stack area for clones to maximum natural alignment
Date: Fri, 12 Apr 2024 00:18:00 +0200
Message-ID: <20240411221800.548140-1-sbrivio@redhat.com>
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CC: runsisi <runsisi@hust.edu.cn>
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Given that we use this stack pointer as a location to store arbitrary
data types from the cloned process, we need to guarantee that its
alignment matches any of those possible data types.
runsisi reports that pasta gets a SIGBUS in pasta_open_ns() on
aarch64, where the alignment requirement for stack pointers is a
16 bytes (same as the size of a long double), and similar requirements
actually apply to most architectures we run on.
Reported-by: runsisi <runsisi@hust.edu.cn>
Link: https://bugs.passt.top/show_bug.cgi?id=85
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
pasta.c | 3 ++-
util.h | 4 +++-
2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/pasta.c b/pasta.c
index e73b5af..31e1e00 100644
--- a/pasta.c
+++ b/pasta.c
@@ -211,12 +211,13 @@ static int pasta_spawn_cmd(void *arg)
void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
int argc, char *argv[])
{
+ char ns_fn_stack[NS_FN_STACK_SIZE]
+ __attribute__ ((aligned(__alignof__(max_align_t))));
struct pasta_spawn_cmd_arg arg = {
.exe = argv[0],
.argv = argv,
};
char uidmap[BUFSIZ], gidmap[BUFSIZ];
- char ns_fn_stack[NS_FN_STACK_SIZE];
char *sh_argv[] = { NULL, NULL };
char sh_arg0[PATH_MAX + 1];
sigset_t set;
diff --git a/util.h b/util.h
index 7c261d7..8c37729 100644
--- a/util.h
+++ b/util.h
@@ -9,6 +9,7 @@
#include <stdlib.h>
#include <stdarg.h>
#include <stdbool.h>
+#include <stddef.h>
#include <string.h>
#include <signal.h>
@@ -116,7 +117,8 @@ int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
void *arg);
#define NS_CALL(fn, arg) \
do { \
- char ns_fn_stack[NS_FN_STACK_SIZE]; \
+ char ns_fn_stack[NS_FN_STACK_SIZE] \
+ __attribute__ ((aligned(__alignof__(max_align_t)))); \
\
do_clone((fn), ns_fn_stack, sizeof(ns_fn_stack), \
CLONE_VM | CLONE_VFORK | CLONE_FILES | SIGCHLD,\
--
2.43.0