linux-kernel - [PATCH] riscv: Improve KASAN

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Message-Id: <20210226125933.32023-1-alex@ghiti.fr>
Date:   Fri, 26 Feb 2021 07:59:33 -0500
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nylon Chen <nylon7@...estech.com>,
        Nick Hu <nickhu@...estech.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Cc:     Alexandre Ghiti <alex@...ti.fr>
Subject: [PATCH] riscv: Improve KASAN_VMALLOC support

When KASAN vmalloc region is populated, there is no userspace process and
the page table in use is swapper_pg_dir, so there is no need to read
SATP. Then we can use the same scheme used by kasan_populate_p*d
functions to go through the page table, which harmonizes the code.

In addition, make use of set_pgd that goes through all unused page table
levels, contrary to p*d_populate functions, which makes this function work
whatever the number of page table levels.

And finally, make sure the writes to swapper_pg_dir are visible using
an sfence.vma.

Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
---
 arch/riscv/mm/kasan_init.c | 59 ++++++++++++--------------------------
 1 file changed, 19 insertions(+), 40 deletions(-)

diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
index e3d91f334b57..b0cee8d35938 100644
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -11,18 +11,6 @@
 #include <asm/fixmap.h>
 #include <asm/pgalloc.h>
 
-static __init void *early_alloc(size_t size, int node)
-{
-	void *ptr = memblock_alloc_try_nid(size, size,
-		__pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_ACCESSIBLE, node);
-
-	if (!ptr)
-		panic("%pS: Failed to allocate %zu bytes align=%zx nid=%d from=%llx\n",
-			__func__, size, size, node, (u64)__pa(MAX_DMA_ADDRESS));
-
-	return ptr;
-}
-
 extern pgd_t early_pg_dir[PTRS_PER_PGD];
 asmlinkage void __init kasan_early_init(void)
 {
@@ -155,38 +143,29 @@ static void __init kasan_populate(void *start, void *end)
 	memset(start, KASAN_SHADOW_INIT, end - start);
 }
 
+void __init kasan_shallow_populate_pgd(unsigned long vaddr, unsigned long end)
+{
+	unsigned long next;
+	void *p;
+	pgd_t *pgd_k = pgd_offset_k(vaddr);
+
+	do {
+		next = pgd_addr_end(vaddr, end);
+		if (pgd_page_vaddr(*pgd_k) == (unsigned long)lm_alias(kasan_early_shadow_pmd)) {
+			p = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+			set_pgd(pgd_k, pfn_pgd(PFN_DOWN(__pa(p)), PAGE_TABLE));
+		}
+	} while (pgd_k++, vaddr = next, vaddr != end);
+}
+
 void __init kasan_shallow_populate(void *start, void *end)
 {
 	unsigned long vaddr = (unsigned long)start & PAGE_MASK;
 	unsigned long vend = PAGE_ALIGN((unsigned long)end);
-	unsigned long pfn;
-	int index;
-	void *p;
-	pud_t *pud_dir, *pud_k;
-	pgd_t *pgd_dir, *pgd_k;
-	p4d_t *p4d_dir, *p4d_k;
-
-	while (vaddr < vend) {
-		index = pgd_index(vaddr);
-		pfn = csr_read(CSR_SATP) & SATP_PPN;
-		pgd_dir = (pgd_t *)pfn_to_virt(pfn) + index;
-		pgd_k = init_mm.pgd + index;
-		pgd_dir = pgd_offset_k(vaddr);
-		set_pgd(pgd_dir, *pgd_k);
-
-		p4d_dir = p4d_offset(pgd_dir, vaddr);
-		p4d_k  = p4d_offset(pgd_k, vaddr);
-
-		vaddr = (vaddr + PUD_SIZE) & PUD_MASK;
-		pud_dir = pud_offset(p4d_dir, vaddr);
-		pud_k = pud_offset(p4d_k, vaddr);
-
-		if (pud_present(*pud_dir)) {
-			p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
-			pud_populate(&init_mm, pud_dir, p);
-		}
-		vaddr += PAGE_SIZE;
-	}
+
+	kasan_shallow_populate_pgd(vaddr, vend);
+
+	local_flush_tlb_all();
 }
 
 void __init kasan_init(void)
-- 
2.20.1