Re: [PATCH v2 1/2] mm/ksm: fix ksm exec support for prctl

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On 22.03.24 07:09, Jinjiang Tu wrote:
commit 3c6f33b7273a ("mm/ksm: support fork/exec for prctl") inherits
MMF_VM_MERGE_ANY flag when a task calls execve(). Howerver, it doesn't
create the mm_slot, so ksmd will not try to scan this task.

To fix it, allocate and add the mm_slot to ksm_mm_head in __bprm_mm_init()
when the mm has MMF_VM_MERGE_ANY flag.

Fixes: 3c6f33b7273a ("mm/ksm: support fork/exec for prctl")
Signed-off-by: Jinjiang Tu <tujinjiang@xxxxxxxxxx>
---
  fs/exec.c           | 10 ++++++++++
  include/linux/ksm.h | 13 +++++++++++++
  2 files changed, 23 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index ff6f26671cfc..66202d016a0a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -67,6 +67,7 @@
  #include <linux/time_namespace.h>
  #include <linux/user_events.h>
  #include <linux/rseq.h>
+#include <linux/ksm.h>
#include <linux/uaccess.h>
  #include <asm/mmu_context.h>
@@ -267,6 +268,13 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
  		goto err_free;
  	}
+ /*
+	 * Need to be called with mmap write lock
+	 * held, to avoid race with ksmd.
+	*/
+	if (ksm_execve(mm))
+		goto err_ksm;
+

But now, would we revert what insert_vm_struct() did?

We're freeing the VMA later, but we might have accounted memory.


What would be cleaner is doing the ksm_execve() before the insert_vm_struct(), and then cleaning up in case insert_vm_struct() failed.

--
Cheers,

David / dhildenb





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