UBUNTU-CVE-2024-44943
In the Linux kernel, the following vulnerability has been resolved: mm: gup: stop abusing try_grab_folio A kernel warning was reported when pinning folio in CMA memory when launching SEV virtual machine. The splat looks like: [ 464.325306] WARNING: CPU: 13 PID: 6734 at mm/gup.c:1313 __get_user_pages+0x423/0x520 [ 464.325464] CPU: 13 PID: 6734 Comm: qemu-kvm Kdump: loaded Not tainted 6.6.33+ #6 [ 464.325477] RIP: 0010:__get_user_pages+0x423/0x520 [ 464.325515] Call Trace: [ 464.325520] <TASK> [ 464.325523] ? __get_user_pages+0x423/0x520 [ 464.325528] ? __warn+0x81/0x130 [ 464.325536] ? __get_user_pages+0x423/0x520 [ 464.325541] ? report_bug+0x171/0x1a0 [ 464.325549] ? handle_bug+0x3c/0x70 [ 464.325554] ? exc_invalid_op+0x17/0x70 [ 464.325558] ? asm_exc_invalid_op+0x1a/0x20 [ 464.325567] ? __get_user_pages+0x423/0x520 [ 464.325575] __gup_longterm_locked+0x212/0x7a0 [ 464.325583] internal_get_user_pages_fast+0xfb/0x190 [ 464.325590] pin_user_pages_fast+0x47/0x60 [ 464.325598] sev_pin_memory+0xca/0x170 [kvm_amd] [ 464.325616] sev_mem_enc_register_region+0x81/0x130 [kvm_amd] Per the analysis done by yangge, when starting the SEV virtual machine, it will call pin_user_pages_fast(..., FOLL_LONGTERM, ...) to pin the memory. But the page is in CMA area, so fast GUP will fail then fallback to the slow path due to the longterm pinnalbe check in try_grab_folio(). The slow path will try to pin the pages then migrate them out of CMA area. But the slow path also uses try_grab_folio() to pin the page, it will also fail due to the same check then the above warning is triggered. In addition, the try_grab_folio() is supposed to be used in fast path and it elevates folio refcount by using add ref unless zero. We are guaranteed to have at least one stable reference in slow path, so the simple atomic add could be used. The performance difference should be trivial, but the misuse may be confusing and misleading. Redefined try_grab_folio() to try_grab_folio_fast(), and try_grab_page() to try_grab_folio(), and use them in the proper paths. This solves both the abuse and the kernel warning. The proper naming makes their usecase more clear and should prevent from abusing in the future. peterx said: : The user will see the pin fails, for gpu-slow it further triggers the WARN : right below that failure (as in the original report): : : folio = try_grab_folio(page, page_increm - 1, : foll_flags); : if (WARN_ON_ONCE(!folio)) { <------------------------ here : /* : * Release the 1st page ref if the : * folio is problematic, fail hard. : */ : gup_put_folio(page_folio(page), 1, : foll_flags); : ret = -EFAULT; : goto out; : } [1] https://lore.kernel.org/linux-mm/[email protected]/ [[email protected]: fix implicit declaration of function try_grab_folio_fast]
02 / AFFECTED SOFTWARE
Affected packages
7 explicit affected versions
29 explicit affected versions
14 explicit affected versions
10 explicit affected versions
11 explicit affected versions
1 explicit affected versions
11 explicit affected versions
7 explicit affected versions
10 explicit affected versions
26 explicit affected versions
9 explicit affected versions
37 explicit affected versions
10 explicit affected versions
10 explicit affected versions
13 explicit affected versions
13 explicit affected versions
8 explicit affected versions
37 explicit affected versions
8 explicit affected versions
4 explicit affected versions
8 explicit affected versions
19 explicit affected versions
23 explicit affected versions
7 explicit affected versions
10 explicit affected versions
14 explicit affected versions
1 explicit affected versions
33 explicit affected versions
16 explicit affected versions
13 explicit affected versions
12 explicit affected versions
38 explicit affected versions
51 explicit affected versions
13 explicit affected versions
10 explicit affected versions
16 explicit affected versions
8 explicit affected versions
10 explicit affected versions
14 explicit affected versions
16 explicit affected versions
13 explicit affected versions
17 explicit affected versions
1 explicit affected versions
10 explicit affected versions
8 explicit affected versions
13 explicit affected versions
21 explicit affected versions
6 explicit affected versions
13 explicit affected versions
12 explicit affected versions
7 explicit affected versions
14 explicit affected versions
16 explicit affected versions
12 explicit affected versions
12 explicit affected versions
10 explicit affected versions
26 explicit affected versions
17 explicit affected versions
23 explicit affected versions
14 explicit affected versions
5 explicit affected versions
3 explicit affected versions
26 explicit affected versions
12 explicit affected versions
44 explicit affected versions
4 explicit affected versions
4 explicit affected versions
18 explicit affected versions
16 explicit affected versions
9 explicit affected versions
12 explicit affected versions
13 explicit affected versions
7 explicit affected versions
17 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
10 explicit affected versions
9 explicit affected versions
14 explicit affected versions
18 explicit affected versions
3 explicit affected versions
16 explicit affected versions
43 explicit affected versions
7 explicit affected versions
11 explicit affected versions
35 explicit affected versions
12 explicit affected versions
13 explicit affected versions
9 explicit affected versions
6 explicit affected versions
12 explicit affected versions
50 explicit affected versions
14 explicit affected versions
12 explicit affected versions
27 explicit affected versions
12 explicit affected versions
7 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: mm: gup: stop abusing try_grab_folio A kernel warning was reported when pinning folio in CMA memory when launching SEV virtual machine. The splat looks like: [ 464.325306] WARNING: CPU: 13 PID: 6734 at mm/gup.c:1313 __get_user_pages+0x423/0x520 [ 464.325464] CPU: 13 PID: 6734 Comm: qemu-kvm Kdump: loaded Not tainted 6.6.33+ #6 [ 464.325477] RIP: 0010:__get_user_pages+0x423/0x520 [ 464.325515] Call Trace: [ 464.325520] <TASK> [ 464.325523] ? __get_user_pages+0x423/0x520 [ 464.325528] ? __warn+0x81/0x130 [ 464.325536] ? __get_user_pages+0x423/0x520 [ 464.325541] ? report_bug+0x171/0x1a0 [ 464.325549] ? handle_bug+0x3c/0x70 [ 464.325554] ? exc_invalid_op+0x17/0x70 [ 464.325558] ? asm_exc_invalid_op+0x1a/0x20 [ 464.325567] ? __get_user_pages+0x423/0x520 [ 464.325575] __gup_longterm_locked+0x212/0x7a0 [ 464.325583] internal_get_user_pages_fast+0xfb/0x190 [ 464.325590] pin_user_pages_fast+0x47/0x60 [ 464.325598] sev_pin_memory+0xca/0x170 [kvm_amd] [ 464.325616] sev_mem_enc_register_region+0x81/0x130 [kvm_amd] Per the analysis done by yangge, when starting the SEV virtual machine, it will call pin_user_pages_fast(..., FOLL_LONGTERM, ...) to pin the memory. But the page is in CMA area, so fast GUP will fail then fallback to the slow path due to the longterm pinnalbe check in try_grab_folio(). The slow path will try to pin the pages then migrate them out of CMA area. But the slow path also uses try_grab_folio() to pin the page, it will also fail due to the same check then the above warning is triggered. In addition, the try_grab_folio() is supposed to be used in fast path and it elevates folio refcount by using add ref unless zero. We are guaranteed to have at least one stable reference in slow path, so the simple atomic add could be used. The performance difference should be trivial, but the misuse may be confusing and misleading. Redefined try_grab_folio() to try_grab_folio_fast(), and try_grab_page() to try_grab_folio(), and use them in the proper paths. This solves both the abuse and the kernel warning. The proper naming makes their usecase more clear and should prevent from abusing in the future. peterx said: : The user will see the pin fails, for gpu-slow it further triggers the WARN : right below that failure (as in the original report): : : folio = try_grab_folio(page, page_increm - 1, : foll_flags); : if (WARN_ON_ONCE(!folio)) { <------------------------ here : /* : * Release the 1st page ref if the : * folio is problematic, fail hard. : */ : gup_put_folio(page_folio(page), 1, : foll_flags); : ret = -EFAULT; : goto out; : } [1] https://lore.kernel.org/linux-mm/[email protected]/ [[email protected]: fix implicit declaration of function try_grab_folio_fast]
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/f442fa6141379a20b48ae3efabee827a3d260787
- https://git.kernel.org/stable/c/26273f5f4cf68b29414e403837093408a9c98e1f
- https://git.kernel.org/stable/c/f442fa6141379a20b48ae3efabee827a3d260787
- https://ubuntu.com/security/CVE-2024-44943
- https://ubuntu.com/security/notices/USN-7154-1
- https://ubuntu.com/security/notices/USN-7154-2
- https://ubuntu.com/security/notices/USN-7155-1
- https://ubuntu.com/security/notices/USN-7156-1
- https://ubuntu.com/security/notices/USN-7196-1
- https://www.cve.org/CVERecord?id=CVE-2024-44943