linux-kernel - [PATCH] x86/debugfs: Add the EFI pagetable to the debugfs 'page

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Message-Id: <ba158a93f3250e6fca752cff2cfb1fcdd9f2b50c.1517414050.git.luto@kernel.org>
Date:   Wed, 31 Jan 2018 07:56:22 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     linux-mm@...ck.org, Borislav Petkov <bp@...en8.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org, Andy Lutomirski <luto@...nel.org>
Subject: [PATCH] x86/debugfs: Add the EFI pagetable to the debugfs 'page_tables' directory

EFI is complicated enough that being able to view its pagetables is
quite helpful.  Rather than requiring users to fish it out of dmesg
on an appropriately configured kernel, let users view it in debugfs
as well.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/mm/debug_pagetables.c | 32 ++++++++++++++++++++++++++++++++
 arch/x86/platform/efi/efi_64.c |  2 +-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/debug_pagetables.c b/arch/x86/mm/debug_pagetables.c
index 421f2664ffa0..9861797b1fd5 100644
--- a/arch/x86/mm/debug_pagetables.c
+++ b/arch/x86/mm/debug_pagetables.c
@@ -72,6 +72,31 @@ static const struct file_operations ptdump_curusr_fops = {
 };
 #endif
 
+#if defined(CONFIG_EFI) && defined(CONFIG_X86_64)
+extern pgd_t *efi_pgd;
+static struct dentry *pe_efi;
+
+static int ptdump_show_efi(struct seq_file *m, void *v)
+{
+	if (efi_pgd)
+		ptdump_walk_pgd_level_debugfs(m, efi_pgd, false);
+	return 0;
+}
+
+static int ptdump_open_efi(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, ptdump_show_efi, NULL);
+}
+
+static const struct file_operations ptdump_efi_fops = {
+	.owner		= THIS_MODULE,
+	.open		= ptdump_open_efi,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+#endif
+
 static struct dentry *dir, *pe_knl, *pe_curknl;
 
 static int __init pt_dump_debug_init(void)
@@ -94,8 +119,15 @@ static int __init pt_dump_debug_init(void)
 	pe_curusr = debugfs_create_file("current_user", 0400,
 					dir, NULL, &ptdump_curusr_fops);
 	if (!pe_curusr)
+                goto err;
+#endif
+
+#if defined(CONFIG_EFI) && defined(CONFIG_X86_64)
+	pe_efi = debugfs_create_file("efi", 0400, dir, NULL, &ptdump_efi_fops);
+	if (!pe_efi)
 		goto err;
 #endif
+
 	return 0;
 err:
 	debugfs_remove_recursive(dir);
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 2dd15e967c3f..a9734df2c1b7 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -191,7 +191,7 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 	early_code_mapping_set_exec(0);
 }
 
-static pgd_t *efi_pgd;
+pgd_t *efi_pgd;
 
 /*
  * We need our own copy of the higher levels of the page tables
-- 
2.14.3