[PATCH 11/30] x86, kaiser: make sure static PGDs are 8k in size

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

A few PGDs come out of the kernel binary instead of being
allocated dynamically.  Before this patch, they are all
8k-aligned, but they must also be 8k in *size*.

The original KAISER patch did not do this.  It probably just
lucked out that it did not trample over data after the last PGD.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Moritz Lipp <moritz.lipp@xxxxxxxxxxxxxx>
Cc: Daniel Gruss <daniel.gruss@xxxxxxxxxxxxxx>
Cc: Michael Schwarz <michael.schwarz@xxxxxxxxxxxxxx>
Cc: Richard Fellner <richard.fellner@xxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
---

 b/arch/x86/kernel/head_64.S |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff -puN arch/x86/kernel/head_64.S~kaiser-head_S-pgds-need-8k-too arch/x86/kernel/head_64.S
--- a/arch/x86/kernel/head_64.S~kaiser-head_S-pgds-need-8k-too	2017-11-10 11:22:11.018244945 -0800
+++ b/arch/x86/kernel/head_64.S	2017-11-10 11:22:11.021244945 -0800
@@ -340,11 +340,24 @@ GLOBAL(early_recursion_flag)
 GLOBAL(name)
 
 #ifdef CONFIG_KAISER
+/*
+ * Each PGD needs to be 8k long and 8k aligned.  We do not
+ * ever go out to userspace with these, so we do not
+ * strictly *need* the second page, but this allows us to
+ * have a single set_pgd() implementation that does not
+ * need to worry about whether it has 4k or 8k to work
+ * with.
+ *
+ * This ensures PGDs are 8k long:
+ */
+#define KAISER_USER_PGD_FILL	512
+/* This ensures they are 8k-aligned: */
 #define NEXT_PGD_PAGE(name) \
 	.balign 2 * PAGE_SIZE; \
 GLOBAL(name)
 #else
 #define NEXT_PGD_PAGE(name) NEXT_PAGE(name)
+#define KAISER_USER_PGD_FILL	0
 #endif
 
 /* Automate the creation of 1 to 1 mapping pmd entries */
@@ -363,6 +376,7 @@ NEXT_PGD_PAGE(early_top_pgt)
 #else
 	.quad	level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
 #endif
+	.fill	KAISER_USER_PGD_FILL,8,0
 
 NEXT_PAGE(early_dynamic_pgts)
 	.fill	512*EARLY_DYNAMIC_PAGE_TABLES,8,0
@@ -372,6 +386,7 @@ NEXT_PAGE(early_dynamic_pgts)
 #ifndef CONFIG_XEN
 NEXT_PGD_PAGE(init_top_pgt)
 	.fill	512,8,0
+	.fill	KAISER_USER_PGD_FILL,8,0
 #else
 NEXT_PGD_PAGE(init_top_pgt)
 	.quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
@@ -380,6 +395,7 @@ NEXT_PGD_PAGE(init_top_pgt)
 	.org    init_top_pgt + PGD_START_KERNEL*8, 0
 	/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
 	.quad   level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
+	.fill	KAISER_USER_PGD_FILL,8,0
 
 NEXT_PAGE(level3_ident_pgt)
 	.quad	level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
_