[PATCH v3 1/2] arm64: ptdump: Make note_page_flush() range aware

[Wei-Lin Chang <weilin.chang@arm.com>]

note_page_flush() calls note_page() with addr == 0 and level == -1 to
dump the last row of a ptdump. addr == 0 (1 << 64 wrapped around)
renders a huge region with enormous size for address spaces with
IA bits < 64. For example the stage-2 page tables and the EFI runtime
page table.

More importantly, the last region of the address space and everything
after the address space up to 1 << 64 are merged into one row of
output. If the last region within the address space is valid, it will
appear to remain valid up to 1 << 64 with the same attributes.

Currently only the EFI runtime ptdump is affected by this, but KVM will
soon fix its stage-2 ptdump by using note_page_flush(). Here is an
example of an EFI runtime ptdump (last row):

0x0000008000000000-0x0000000000000000   17179868672G PGD

With this patch:

0x0000008000000000-0x0001000000000000      261632G PGD

To fix this, cache the end address of a ptdump in ptdump_pg_state so
note_page_flush() can call the final note_page() with the correct end
address.

Fixes: 9d80448ac92b ("efi/arm64: Add debugfs node to dump UEFI runtime page tables")
Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
---
 arch/arm64/include/asm/ptdump.h |  2 ++
 arch/arm64/mm/ptdump.c          | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
index 5b374a6ab34a..1b743de7d89e 100644
--- a/arch/arm64/include/asm/ptdump.h
+++ b/arch/arm64/include/asm/ptdump.h
@@ -52,6 +52,8 @@ struct ptdump_pg_state {
 	const struct addr_marker *marker;
 	const struct mm_struct *mm;
 	unsigned long start_address;
+	/* exclusive end, ULONG_MAX represents an end at 1 << 64 */
+	unsigned long end_address;
 	int level;
 	ptval_t current_prot;
 	bool check_wx;
diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index 1c20144700d7..eab400e744d9 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -278,9 +278,19 @@ void note_page_pgd(struct ptdump_state *pt_st, unsigned long addr, pgd_t pgd)
 
 void note_page_flush(struct ptdump_state *pt_st)
 {
+	struct ptdump_pg_state *st = container_of(pt_st, struct ptdump_pg_state, ptdump);
+	unsigned long end = st->end_address;
 	pte_t pte_zero = {0};
 
-	note_page(pt_st, 0, -1, pte_val(pte_zero));
+	/*
+	 * Address spaces that end at 1 << 64 have end_address == ULONG_MAX,
+	 * but note_page() expects the exclusive end. In this case adjust end
+	 * to the wraparound value 0.
+	 */
+	if (end == ULONG_MAX)
+		end = 0;
+
+	note_page(pt_st, end, -1, pte_val(pte_zero));
 }
 
 static void arm64_ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
@@ -303,6 +313,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info)
 		.marker = info->markers,
 		.mm = info->mm,
 		.pg_level = &kernel_pg_levels[0],
+		.end_address = end,
 		.level = -1,
 		.ptdump = {
 			.note_page_pte = note_page_pte,
@@ -344,6 +355,7 @@ bool ptdump_check_wx(void)
 			{ -1, NULL},
 		},
 		.pg_level = &kernel_pg_levels[0],
+		.end_address = ~0UL,
 		.level = -1,
 		.check_wx = true,
 		.ptdump = {
-- 
2.43.0