On 2024/4/4 5:21, David Hildenbrand wrote:
> PAT handling won't do the right thing in COW mappings: the first PTE
> (or, in fact, all PTEs) can be replaced during write faults to point at
> anon folios. Reliably recovering the correct PFN and cachemode using
> follow_phys() from PTEs will not work in COW mappings.
>
> Using follow_phys(), we might just get the address+protection of the
> anon folio (which is very wrong), or fail on swap/nonswap entries,
> failing follow_phys() and triggering a WARN_ON_ONCE() in untrack_pfn()
> and track_pfn_copy(), not properly calling free_pfn_range().
>
> In free_pfn_range(), we either wouldn't call memtype_free() or would
> call it with the wrong range, possibly leaking memory.
>
> To fix that, let's update follow_phys() to refuse returning anon folios,
> and fallback to using the stored PFN inside vma->vm_pgoff for COW
> mappings if we run into that.
>
> We will now properly handle untrack_pfn() with COW mappings, where we
> don't need the cachemode. We'll have to fail fork()->track_pfn_copy() if
> the first page was replaced by an anon folio, though: we'd have to store
> the cachemode in the VMA to make this work, likely growing the VMA size.
>
> For now, lets keep it simple and let track_pfn_copy() just fail in that
> case: it would have failed in the past with swap/nonswap entries already,
> and it would have done the wrong thing with anon folios.
>
> Simple reproducer to trigger the WARN_ON_ONCE() in untrack_pfn():
>
> <--- C reproducer --->
> #include <stdio.h>
> #include <sys/mman.h>
> #include <unistd.h>
> #include <liburing.h>
>
> int main(void)
> {
> struct io_uring_params p = {};
> int ring_fd;
> size_t size;
> char *map;
>
> ring_fd = io_uring_setup(1, &p);
> if (ring_fd < 0) {
> perror("io_uring_setup");
> return 1;
> }
> size = p.sq_off.array + p.sq_entries * sizeof(unsigned);
>
> /* Map the submission queue ring MAP_PRIVATE */
> map = mmap(0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE,
> ring_fd, IORING_OFF_SQ_RING);
> if (map == MAP_FAILED) {
> perror("mmap");
> return 1;
> }
>
> /* We have at least one page. Let's COW it. */
> *map = 0;
> pause();
> return 0;
> }
> <--- C reproducer --->
>
> On a system with 16 GiB RAM and swap configured:
> # ./iouring &
> # memhog 16G
> # killall iouring
> [ 301.552930] ------------[ cut here ]------------
> [ 301.553285] WARNING: CPU: 7 PID: 1402 at arch/x86/mm/pat/memtype.c:1060 untrack_pfn+0xf4/0x100
> [ 301.553989] Modules linked in: binfmt_misc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_g
> [ 301.558232] CPU: 7 PID: 1402 Comm: iouring Not tainted 6.7.5-100.fc38.x86_64 #1
> [ 301.558772] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebu4
> [ 301.559569] RIP: 0010:untrack_pfn+0xf4/0x100
> [ 301.559893] Code: 75 c4 eb cf 48 8b 43 10 8b a8 e8 00 00 00 3b 6b 28 74 b8 48 8b 7b 30 e8 ea 1a f7 000
> [ 301.561189] RSP: 0018:ffffba2c0377fab8 EFLAGS: 00010282
> [ 301.561590] RAX: 00000000ffffffea RBX: ffff9208c8ce9cc0 RCX: 000000010455e047
> [ 301.562105] RDX: 07fffffff0eb1e0a RSI: 0000000000000000 RDI: ffff9208c391d200
> [ 301.562628] RBP: 0000000000000000 R08: ffffba2c0377fab8 R09: 0000000000000000
> [ 301.563145] R10: ffff9208d2292d50 R11: 0000000000000002 R12: 00007fea890e0000
> [ 301.563669] R13: 0000000000000000 R14: ffffba2c0377fc08 R15: 0000000000000000
> [ 301.564186] FS: 0000000000000000(0000) GS:ffff920c2fbc0000(0000) knlGS:0000000000000000
> [ 301.564773] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 301.565197] CR2: 00007fea88ee8a20 CR3: 00000001033a8000 CR4: 0000000000750ef0
> [ 301.565725] PKRU: 55555554
> [ 301.565944] Call Trace:
> [ 301.566148] <TASK>
> [ 301.566325] ? untrack_pfn+0xf4/0x100
> [ 301.566618] ? __warn+0x81/0x130
> [ 301.566876] ? untrack_pfn+0xf4/0x100
> [ 301.567163] ? report_bug+0x171/0x1a0
> [ 301.567466] ? handle_bug+0x3c/0x80
> [ 301.567743] ? exc_invalid_op+0x17/0x70
> [ 301.568038] ? asm_exc_invalid_op+0x1a/0x20
> [ 301.568363] ? untrack_pfn+0xf4/0x100
> [ 301.568660] ? untrack_pfn+0x65/0x100
> [ 301.568947] unmap_single_vma+0xa6/0xe0
> [ 301.569247] unmap_vmas+0xb5/0x190
> [ 301.569532] exit_mmap+0xec/0x340
> [ 301.569801] __mmput+0x3e/0x130
> [ 301.570051] do_exit+0x305/0xaf0
> ...
>
> Reported-by: Wupeng Ma <mawupeng1@xxxxxxxxxx>
> Closes: https://lkml.kernel.org/r/20240227122814.3781907-1-mawupeng1@xxxxxxxxxx
> Fixes: b1a86e15dc03 ("x86, pat: remove the dependency on 'vm_pgoff' in track/untrack pfn vma routines")
> Fixes: 5899329b1910 ("x86: PAT: implement track/untrack of pfnmap regions for x86 - v3")
> Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> arch/x86/mm/pat/memtype.c | 49 ++++++++++++++++++++++++++++-----------
> mm/memory.c | 4 ++++
> 2 files changed, 39 insertions(+), 14 deletions(-
Test-by: Wupeng Ma <mawupeng1@xxxxxxxxxx>
>
> diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
> index 0d72183b5dd0..36b603d0cdde 100644
> --- a/arch/x86/mm/pat/memtype.c
> +++ b/arch/x86/mm/pat/memtype.c
> @@ -947,6 +947,38 @@ static void free_pfn_range(u64 paddr, unsigned long size)
> memtype_free(paddr, paddr + size);
> }
>
> +static int get_pat_info(struct vm_area_struct *vma, resource_size_t *paddr,
> + pgprot_t *pgprot)
> +{
> + unsigned long prot;
> +
> + VM_WARN_ON_ONCE(!(vma->vm_flags & VM_PAT));
> +
> + /*
> + * We need the starting PFN and cachemode used for track_pfn_remap()
> + * that covered the whole VMA. For most mappings, we can obtain that
> + * information from the page tables. For COW mappings, we might now
> + * suddenly have anon folios mapped and follow_phys() will fail.
> + *
> + * Fallback to using vma->vm_pgoff, see remap_pfn_range_notrack(), to
> + * detect the PFN. If we need the cachemode as well, we're out of luck
> + * for now and have to fail fork().
> + */
> + if (!follow_phys(vma, vma->vm_start, 0, &prot, paddr)) {
> + if (pgprot)
> + *pgprot = __pgprot(prot);
> + return 0;
> + }
> + if (is_cow_mapping(vma->vm_flags)) {
> + if (pgprot)
> + return -EINVAL;
> + *paddr = (resource_size_t)vma->vm_pgoff << PAGE_SHIFT;
> + return 0;
> + }
> + WARN_ON_ONCE(1);
> + return -EINVAL;
> +}
> +
> /*
> * track_pfn_copy is called when vma that is covering the pfnmap gets
> * copied through copy_page_range().
> @@ -957,20 +989,13 @@ static void free_pfn_range(u64 paddr, unsigned long size)
> int track_pfn_copy(struct vm_area_struct *vma)
> {
> resource_size_t paddr;
> - unsigned long prot;
> unsigned long vma_size = vma->vm_end - vma->vm_start;
> pgprot_t pgprot;
>
> if (vma->vm_flags & VM_PAT) {
> - /*
> - * reserve the whole chunk covered by vma. We need the
> - * starting address and protection from pte.
> - */
> - if (follow_phys(vma, vma->vm_start, 0, &prot, &paddr)) {
> - WARN_ON_ONCE(1);
> + if (get_pat_info(vma, &paddr, &pgprot))
> return -EINVAL;
> - }
> - pgprot = __pgprot(prot);
> + /* reserve the whole chunk covered by vma. */
> return reserve_pfn_range(paddr, vma_size, &pgprot, 1);
> }
>
> @@ -1045,7 +1070,6 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
> unsigned long size, bool mm_wr_locked)
> {
> resource_size_t paddr;
> - unsigned long prot;
>
> if (vma && !(vma->vm_flags & VM_PAT))
> return;
> @@ -1053,11 +1077,8 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
> /* free the chunk starting from pfn or the whole chunk */
> paddr = (resource_size_t)pfn << PAGE_SHIFT;
> if (!paddr && !size) {
> - if (follow_phys(vma, vma->vm_start, 0, &prot, &paddr)) {
> - WARN_ON_ONCE(1);
> + if (get_pat_info(vma, &paddr, NULL))
> return;
> - }
> -
> size = vma->vm_end - vma->vm_start;
> }
> free_pfn_range(paddr, size);
> diff --git a/mm/memory.c b/mm/memory.c
> index 1211e2090c1a..1e9a0288fdaf 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6002,6 +6002,10 @@ int follow_phys(struct vm_area_struct *vma,
> goto out;
> pte = ptep_get(ptep);
>
> + /* Never return PFNs of anon folios in COW mappings. */
> + if (vm_normal_folio(vma, address, pte))
> + goto unlock;
> +
> if ((flags & FOLL_WRITE) && !pte_write(pte))
> goto unlock;
>
