riscv: Fix kfence now that the linear mapping can be backed by PUD/P4D/PGD

RISC-V Kfence implementation used to rely on the fact the linear mapping
was backed by at most PMD hugepages, which is not true anymore since
commit 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear
mapping").

Instead of splitting PUD/P4D/PGD mappings afterwards, directly map the
kfence pool region using PTE mappings by allocating this region before
setup_vm_final().

Reported-by: syzbot+a74d57bddabbedd75135@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a74d57bddabbedd75135
Fixes: 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20230606130444.25090-1-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 0 insertions, 33 deletions

diff --git a/arch/riscv/include/asm/kfence.h b/arch/riscv/include/asm/kfence.h
index d887a54042aa..0bbffd528096 100644
--- a/arch/riscv/include/asm/kfence.h
+++ b/arch/riscv/include/asm/kfence.h
@@ -8,41 +8,8 @@
 #include <asm-generic/pgalloc.h>
 #include <asm/pgtable.h>
 
-static inline int split_pmd_page(unsigned long addr)
-{
-	int i;
-	unsigned long pfn = PFN_DOWN(__pa((addr & PMD_MASK)));
-	pmd_t *pmd = pmd_off_k(addr);
-	pte_t *pte = pte_alloc_one_kernel(&init_mm);
-
-	if (!pte)
-		return -ENOMEM;
-
-	for (i = 0; i < PTRS_PER_PTE; i++)
-		set_pte(pte + i, pfn_pte(pfn + i, PAGE_KERNEL));
-	set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa(pte)), PAGE_TABLE));
-
-	flush_tlb_kernel_range(addr, addr + PMD_SIZE);
-	return 0;
-}
-
 static inline bool arch_kfence_init_pool(void)
 {
-	int ret;
-	unsigned long addr;
-	pmd_t *pmd;
-
-	for (addr = (unsigned long)__kfence_pool; is_kfence_address((void *)addr);
-	     addr += PAGE_SIZE) {
-		pmd = pmd_off_k(addr);
-
-		if (pmd_leaf(*pmd)) {
-			ret = split_pmd_page(addr);
-			if (ret)
-				return false;
-		}
-	}
-
 	return true;
 }