On Fri, Apr 12, 2024 at 12:18:00AM +0200, Stefano Brivio wrote:

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 Link: https://bugs.passt.top/show_bug.cgi?id=85 Signed-off-by: Stefano Brivio

Reviewed-by: David Gibson

--- 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 #include #include +#include #include #include

@@ -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,\

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