Re: [PATCH bpf v2 2/4] bpf_trace: support 32-bit kernels in bpf_kprobe_multi_link_attach

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On 5/16/22 4:05 PM, Eugene Syromiatnikov wrote:
It seems that there is no reason not to support 32-bit architectures;
doing so requires a bit of rework with respect to cookies handling,
however, as the current code implicitly assumes
that sizeof(long) == sizeof(u64).

Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
---
  kernel/trace/bpf_trace.c | 18 +++++++++---------
  1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f1d4e68..bf5bcfb 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2406,16 +2406,12 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
  	struct bpf_link_primer link_primer;
  	void __user *ucookies;
  	unsigned long *addrs;
-	u32 flags, cnt, size;
+	u32 flags, cnt, size, cookies_size;
  	void __user *uaddrs;
  	u64 *cookies = NULL;
  	void __user *usyms;
  	int err;
- /* no support for 32bit archs yet */
-	if (sizeof(u64) != sizeof(void *))
-		return -EOPNOTSUPP;
-
  	if (prog->expected_attach_type != BPF_TRACE_KPROBE_MULTI)
  		return -EINVAL;
@@ -2425,6 +2421,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr uaddrs = u64_to_user_ptr(attr->link_create.kprobe_multi.addrs);
  	usyms = u64_to_user_ptr(attr->link_create.kprobe_multi.syms);
+	ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
  	if (!!uaddrs == !!usyms)
  		return -EINVAL;
@@ -2432,8 +2429,11 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
  	if (!cnt)
  		return -EINVAL;
- if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
+	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size) ||
+	    (ucookies &&
+	     check_mul_overflow(cnt, (u32)sizeof(*cookies), &cookies_size))) {
  		return -EOVERFLOW;
+	}
  	size = cnt * sizeof(*addrs);

size has been calculated, no need to calculate again.

  	addrs = kvmalloc(size, GFP_KERNEL);
  	if (!addrs)
@@ -2450,14 +2450,14 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
  			goto error;
  	}
- ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
  	if (ucookies) {
-		cookies = kvmalloc(size, GFP_KERNEL);
+		cookies_size = cnt * sizeof(*cookies);

same for cookies_size.

+		cookies = kvmalloc(cookies_size, GFP_KERNEL);
  		if (!cookies) {
  			err = -ENOMEM;
  			goto error;
  		}
-		if (copy_from_user(cookies, ucookies, size)) {
+		if (copy_from_user(cookies, ucookies, cookies_size)) {
  			err = -EFAULT;
  			goto error;
  		}



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