linux-kernel - [PATCH 12/30] x86, kaiser: map GDT into user page tables

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20171110193125.EBF58596@viggo.jf.intel.com>
Date:   Fri, 10 Nov 2017 11:31:25 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, dave.hansen@...ux.intel.com,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        luto@...nel.org, torvalds@...ux-foundation.org,
        keescook@...gle.com, hughd@...gle.com, x86@...nel.org
Subject: [PATCH 12/30] x86, kaiser: map GDT into user page tables


From: Dave Hansen <dave.hansen@...ux.intel.com>

The GDT is used to control the x86 segmentation mechanism.  It
must be virtually mapped when switching segments or at IRET
time when switching between userspace and kernel.

The original KAISER patch did not do this.  I have no idea how
it ever worked.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Moritz Lipp <moritz.lipp@...k.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@...k.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@...k.tugraz.at>
Cc: Richard Fellner <richard.fellner@...dent.tugraz.at>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...gle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: x86@...nel.org
---

 b/arch/x86/kernel/cpu/common.c |   15 +++++++++++++++
 b/arch/x86/mm/kaiser.c         |   10 ++++++++++
 2 files changed, 25 insertions(+)

diff -puN arch/x86/kernel/cpu/common.c~kaiser-user-map-gdt-pages arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~kaiser-user-map-gdt-pages	2017-11-10 11:22:11.559244943 -0800
+++ b/arch/x86/kernel/cpu/common.c	2017-11-10 11:22:11.564244943 -0800
@@ -5,6 +5,7 @@
 #include <linux/export.h>
 #include <linux/percpu.h>
 #include <linux/string.h>
+#include <linux/kaiser.h>
 #include <linux/ctype.h>
 #include <linux/delay.h>
 #include <linux/sched/mm.h>
@@ -487,6 +488,20 @@ static inline void setup_fixmap_gdt(int
 #endif
 
 	__set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
+
+	/* CPU 0's mapping is done in kaiser_init() */
+	if (cpu) {
+		int ret;
+
+		ret = kaiser_add_mapping((unsigned long) get_cpu_gdt_ro(cpu),
+					 PAGE_SIZE, __PAGE_KERNEL_RO);
+		/*
+		 * We do not have a good way to fail CPU bringup.
+		 * Just WARN about it and hope we boot far enough
+		 * to get a good log out.
+		 */
+		WARN_ON(ret);
+	}
 }
 
 /* Load the original GDT from the per-cpu structure */
diff -puN arch/x86/mm/kaiser.c~kaiser-user-map-gdt-pages arch/x86/mm/kaiser.c
--- a/arch/x86/mm/kaiser.c~kaiser-user-map-gdt-pages	2017-11-10 11:22:11.560244943 -0800
+++ b/arch/x86/mm/kaiser.c	2017-11-10 11:22:11.565244943 -0800
@@ -372,6 +372,16 @@ void __init kaiser_init(void)
 	kaiser_add_user_map_early((void *)idt_descr.address,
 				  sizeof(gate_desc) * NR_VECTORS,
 				  __PAGE_KERNEL_RO | _PAGE_GLOBAL);
+
+	/*
+	 * We could theoretically do this in setup_fixmap_gdt().
+	 * But, we would need to rewrite the above page table
+	 * allocation code to use the bootmem allocator.  The
+	 * buddy allocator is not available at the time that we
+	 * call setup_fixmap_gdt() for CPU 0.
+	 */
+	kaiser_add_user_map_early(get_cpu_gdt_ro(0), PAGE_SIZE,
+				  __PAGE_KERNEL_RO | _PAGE_GLOBAL);
 }
 
 int kaiser_add_mapping(unsigned long addr, unsigned long size,
_