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From:   zhenwei pi <pizhenwei@bytedance.com>
To:     pizhenwei@bytedance.com, naoya.horiguchi@nec.com,
        akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        David Hildenbrand <david@redhat.com>
Subject: [PATCH v3 1/1] mm/memory-failure: don't allow to unpoison hw corrupted page
Date:   Fri, 10 Jun 2022 19:46:46 +0800
Message-Id: <20220610114646.162764-2-pizhenwei@bytedance.com>
In-Reply-To: <20220610114646.162764-1-pizhenwei@bytedance.com>
References: <20220610114646.162764-1-pizhenwei@bytedance.com>
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Currently unpoison_memory(unsigned long pfn) is designed for soft
poison(hwpoison-inject) only. Since 17fae1294ad9d, the KPTE gets
cleared on a x86 platform once hardware memory corrupts.

Unpoisoning a hardware corrupted page puts page back buddy only,
the kernel has a chance to access the page with *NOT PRESENT* KPTE.
This leads BUG during accessing on the corrupted KPTE.

Do not allow to unpoison hardware corrupted page in unpoison_memory() to
avoid BUG like this:

 Unpoison: Software-unpoisoned page 0x61234
 BUG: unable to handle page fault for address: ffff888061234000
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 2c01067 P4D 2c01067 PUD 107267063 PMD 10382b063 PTE 800fffff9edcb062
 Oops: 0002 [#1] PREEMPT SMP NOPTI
 CPU: 4 PID: 26551 Comm: stress Kdump: loaded Tainted: G   M       OE     5.18.0.bm.1-amd64 #7
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ...
 RIP: 0010:clear_page_erms+0x7/0x10
 Code: ...
 RSP: 0000:ffffc90001107bc8 EFLAGS: 00010246
 RAX: 0000000000000000 RBX: 0000000000000901 RCX: 0000000000001000
 RDX: ffffea0001848d00 RSI: ffffea0001848d40 RDI: ffff888061234000
 RBP: ffffea0001848d00 R08: 0000000000000901 R09: 0000000000001276
 R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000001
 R13: 0000000000000000 R14: 0000000000140dca R15: 0000000000000001
 FS:  00007fd8b2333740(0000) GS:ffff88813fd00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: ffff888061234000 CR3: 00000001023d2005 CR4: 0000000000770ee0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 PKRU: 55555554
 Call Trace:
  <TASK>
  prep_new_page+0x151/0x170
  get_page_from_freelist+0xca0/0xe20
  ? sysvec_apic_timer_interrupt+0xab/0xc0
  ? asm_sysvec_apic_timer_interrupt+0x1b/0x20
  __alloc_pages+0x17e/0x340
  __folio_alloc+0x17/0x40
  vma_alloc_folio+0x84/0x280
  __handle_mm_fault+0x8d4/0xeb0
  handle_mm_fault+0xd5/0x2a0
  do_user_addr_fault+0x1d0/0x680
  ? kvm_read_and_reset_apf_flags+0x3b/0x50
  exc_page_fault+0x78/0x170
  asm_exc_page_fault+0x27/0x30

Fixes: 847ce401df392 ("HWPOISON: Add unpoisoning support")
Fixes: 17fae1294ad9d ("x86/{mce,mm}: Unmap the entire page if the whole page is affected and poisoned")
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 mm/memory-failure.c | 59 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index b85661cbdc4a..3124f428302c 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2068,6 +2068,58 @@ static int __init memory_failure_init(void)
 }
 core_initcall(memory_failure_init);
 
+/*
+ * Unpoisoning a hardware corrupted page with *NOT PRESENT* KPTE leads panic.
+ * Test a page is valid in the kernel mapping.
+ */
+static bool kmap_valid(struct page *page)
+{
+	unsigned long addr = (unsigned long)page_to_virt(page);
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	pgd = pgd_offset_k(addr);
+	if (pgd_none(*pgd))
+		return false;
+	if (pgd_leaf(*pgd))
+		return true;
+	if (pgd_bad(*pgd))
+		return false;
+
+	p4d = p4d_offset(pgd, addr);
+	if (p4d_none(*p4d))
+		return false;
+	if (p4d_leaf(*p4d))
+		return true;
+	if (p4d_bad(*p4d))
+		return false;
+
+	pud = pud_offset(p4d, addr);
+	if (pud_none(*pud))
+		return false;
+	if (pud_leaf(*pud))
+		return true;
+	if (pud_bad(*pud))
+		return false;
+
+	pmd = pmd_offset(pud, addr);
+	if (pmd_none(*pmd))
+		return false;
+	if (pmd_leaf(*pmd))
+		return true;
+	if (pmd_bad(*pmd))
+		return false;
+
+	pte = pte_offset_map(pmd, addr);
+	if (pte_none(*pte) || !pte_present(*pte))
+		return false;
+
+	return true;
+}
+
 #define unpoison_pr_info(fmt, pfn, rs)			\
 ({							\
 	if (__ratelimit(rs))				\
@@ -2109,6 +2161,13 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
+	if (!kmap_valid(page)) {
+		unpoison_pr_info("Unpoison: Page was hardware poisoned %#lx\n",
+				 pfn, &unpoison_rs);
+		ret = -EOPNOTSUPP;
+		goto unlock_mutex;
+	}
+
 	if (page_count(page) > 1) {
 		unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx\n",
 				 pfn, &unpoison_rs);
-- 
2.20.1