On Sun, Jul 9, 2023 at 6:32 AM Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sun, Jul 09, 2023 at 02:39:00PM +0200, Thorsten Leemhuis wrote:
On 09.07.23 13:14, Greg Kroah-Hartman wrote:
From: Suren Baghdasaryan surenb@google.com
commit 2b4f3b4987b56365b981f44a7e843efa5b6619b9 upstream.
Patch series "Avoid memory corruption caused by per-VMA locks", v4.
A memory corruption was reported in [1] with bisection pointing to the patch [2] enabling per-VMA locks for x86. Based on the reproducer provided in [1] we suspect this is caused by the lack of VMA locking while forking a child process. [...]
Question from someone that is neither a C nor a git expert -- and thus might say something totally stupid below (and thus maybe should not have sent this mail at all).
But I have to wonder: is adding this patch to stable necessary given patch 8/8?
FWIW, this change looks like this:
kernel/fork.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/kernel/fork.c +++ b/kernel/fork.c @@ -662,6 +662,12 @@ static __latent_entropy int dup_mmap(str retval = -EINTR; goto fail_uprobe_end; } +#ifdef CONFIG_PER_VMA_LOCK
- /* Disallow any page faults before calling flush_cache_dup_mm */
- for_each_vma(old_vmi, mpnt)
vma_start_write(mpnt);- vma_iter_set(&old_vmi, 0);
+#endif flush_cache_dup_mm(oldmm); uprobe_dup_mmap(oldmm, mm); /*
But when I look at kernel/fork.c in mainline I can't see this bit. I also only see Linus' change (e.g. patch 8/8 in this series) when I look at https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/kerne...
Look at 946c6b59c56d ("Merge tag 'mm-hotfixes-stable-2023-07-08-10-43' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm")
Where Linus manually dropped those #ifdefs.
Hm, I'll leave them for now in 6.4.y as that is "safer", but if Suren feels comfortable, I'll gladly take a patch from him to drop them in the 6.4.y tree as well.
Hi Greg, Give me a couple hours to get back to my computer. Linus took a different version of this patch and changed the description quite a bit. Once I'm home I can send you the patchset that was merged into his tree. Also let me know if you want to disable CONFIG_PER_VMA_LOCK in the stable branch (the patch called "[PATCH 6.4 1/8] mm: disable CONFIG_PER_VMA_LOCK until its fixed" which Linus did not take AFAIKT). Thanks, Suren.
thanks,
greg k-h