[PATCH v6 0/8] arm: support CONFIG_RODATA

[PATCH v6 0/8] arm: support CONFIG_RODATA

[Kees Cook]

This is a series of patches to support CONFIG_RODATA on ARM, so that
the kernel text is RO, and non-text sections default to NX. To support
on-the-fly kernel text patching (via ftrace, kprobes, etc), fixmap
support has been finalized based on several versions of various patches
that are floating around on the mailing list. This series attempts to
include the least intrusive version, so that others can build on it for
future fixmap work.

The series has been heavily tested, and appears to be working correctly:

With CONFIG_ARM_PTDUMP, expected page table permissions are seen in
/sys/kernel/debug/kernel_page_tables.

Using CONFIG_LKDTM, the kernel now correctly detects bad accesses for
for the following lkdtm tests via /sys/kernel/debug/provoke-crash/DIRECT:
        EXEC_DATA
        WRITE_RO
        WRITE_KERN

ftrace works:
        CONFIG_FTRACE_STARTUP_TEST passes
        Enabling tracing works:
                echo function > /sys/kernel/debug/tracing/current_tracer
kprobes works:
        CONFIG_ARM_KPROBES_TEST passes

kexec works:
        kexec will load and start a new kernel

Built with and without CONFIG_HIGHMEM, CONFIG_HIGHMEM_DEBUG, and
CONFIG_NR_CPUS=32.

Thanks to everyone who has been testing this series and working on its
various pieces!

Hopefully this should address Will's last concerns. :)

Thanks!

-Kees

v6:
- always run patch_text under stop_machine (will.deacon)
- document set_fixmap's TLB flushing situation (will.deacon)

v5:
- clean up #includes in mmu.c (will.deacon)
- optimize get_cr() test (will.deacon)
- created free_tcmmem to avoid excessive #ifdefs (will.deacon)
- explicitly test irqs_disabled in set_fixmap (will.deacon)

v4:
- expanded fixmap to 3MB to support 32 CPUs (robh)
- corrected pmd-finding via vaddr instead of FIXMAP_START (robh)
- switched structure size test to BUILD_BUG_ON (sboyd)
- added locking annotations to keep sparse happy (sboyd)
- adding missing "static" declarations noticed by sparse
- reorganized fixmap portion of patches

v3:
- more cleanups in switch to generic fixmap (lauraa, robh)
- fixed kexec merge hunk glitch (will.deacon)
- added tested-by tags where appropriate from v2 testing

v2:
- fix typo in kexec merge (buildbot)
- flip index order for highmem pte access (lauraa)
- added kgdb updates (dianders)

[PATCH v6 1/8] arm: use generic fixmap.h

[Kees Cook]

From: Mark Salter <msalter@redhat.com>

ARM is different from other architectures in that fixmap pages are indexed
with a positive offset from FIXADDR_START.  Other architectures index with
a negative offset from FIXADDR_TOP.  In order to use the generic fixmap.h
definitions, this patch redefines FIXADDR_TOP to be inclusive of the
useable range.  That is, FIXADDR_TOP is the virtual address of the topmost
fixed page.  The newly defined FIXADDR_END is the first virtual address
past the fixed mappings.

Signed-off-by: Mark Salter <msalter@redhat.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
[kees: update for a05e54c103b0 ("ARM: 8031/2: change fixmap ...")]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Rob Herring <robh@kernel.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/include/asm/fixmap.h | 27 +++++++++------------------
 arch/arm/mm/init.c            |  2 +-
 2 files changed, 10 insertions(+), 19 deletions(-)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 74124b0d0d79..a7add6f9315d 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -2,27 +2,18 @@
 #define _ASM_FIXMAP_H
 
 #define FIXADDR_START		0xffc00000UL
-#define FIXADDR_TOP		0xffe00000UL
-#define FIXADDR_SIZE		(FIXADDR_TOP - FIXADDR_START)
+#define FIXADDR_END		0xffe00000UL
+#define FIXADDR_TOP		(FIXADDR_END - PAGE_SIZE)
 
-#define FIX_KMAP_NR_PTES	(FIXADDR_SIZE >> PAGE_SHIFT)
+#include <asm/kmap_types.h>
 
-#define __fix_to_virt(x)	(FIXADDR_START + ((x) << PAGE_SHIFT))
-#define __virt_to_fix(x)	(((x) - FIXADDR_START) >> PAGE_SHIFT)
+enum fixed_addresses {
+	FIX_KMAP_BEGIN,
+	FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1,
 
-extern void __this_fixmap_does_not_exist(void);
+	__end_of_fixed_addresses
+};
 
-static inline unsigned long fix_to_virt(const unsigned int idx)
-{
-	if (idx >= FIX_KMAP_NR_PTES)
-		__this_fixmap_does_not_exist();
-	return __fix_to_virt(idx);
-}
-
-static inline unsigned int virt_to_fix(const unsigned long vaddr)
-{
-	BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
-	return __virt_to_fix(vaddr);
-}
+#include <asm-generic/fixmap.h>
 
 #endif
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 659c75d808dc..ad82c05bfc3a 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -570,7 +570,7 @@ void __init mem_init(void)
 			MLK(DTCM_OFFSET, (unsigned long) dtcm_end),
 			MLK(ITCM_OFFSET, (unsigned long) itcm_end),
 #endif
-			MLK(FIXADDR_START, FIXADDR_TOP),
+			MLK(FIXADDR_START, FIXADDR_END),
 			MLM(VMALLOC_START, VMALLOC_END),
 			MLM(PAGE_OFFSET, (unsigned long)high_memory),
 #ifdef CONFIG_HIGHMEM
-- 
1.9.1

[PATCH v6 2/8] ARM: expand fixmap region to 3MB

[Kees Cook]

From: Rob Herring <robh@kernel.org>

With commit a05e54c103b0 ("ARM: 8031/2: change fixmap mapping region to
support 32 CPUs"), the fixmap region was expanded to 2MB, but it
precluded any other uses of the fixmap region. In order to support other
uses the fixmap region needs to be expanded beyond 2MB. Fortunately, the
adjacent 1MB range 0xffe00000-0xfff00000 is availabe.

Remove fixmap_page_table ptr and lookup the page table via the virtual
address so that the fixmap region can span more that one pmd. The 2nd
pmd is already created since it is shared with the vector page.

Signed-off-by: Rob Herring <robh@kernel.org>
[kees: fixed CONFIG_DEBUG_HIGHMEM get_fixmap() calls]
[kees: moved pte allocation outside of CONFIG_HIGHMEM]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 Documentation/arm/memory.txt  |  2 +-
 arch/arm/include/asm/fixmap.h |  2 +-
 arch/arm/mm/highmem.c         | 15 ++++++++-------
 arch/arm/mm/mmu.c             |  6 +++---
 4 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/Documentation/arm/memory.txt b/Documentation/arm/memory.txt
index 38dc06d0a791..4178ebda6e66 100644
--- a/Documentation/arm/memory.txt
+++ b/Documentation/arm/memory.txt
@@ -41,7 +41,7 @@ fffe8000	fffeffff	DTCM mapping area for platforms with
 fffe0000	fffe7fff	ITCM mapping area for platforms with
 				ITCM mounted inside the CPU.
 
-ffc00000	ffdfffff	Fixmap mapping region.  Addresses provided
+ffc00000	ffefffff	Fixmap mapping region.  Addresses provided
 				by fix_to_virt() will be located here.
 
 fee00000	feffffff	Mapping of PCI I/O space. This is a static
diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index a7add6f9315d..d984ca69ce19 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -2,7 +2,7 @@
 #define _ASM_FIXMAP_H
 
 #define FIXADDR_START		0xffc00000UL
-#define FIXADDR_END		0xffe00000UL
+#define FIXADDR_END		0xfff00000UL
 #define FIXADDR_TOP		(FIXADDR_END - PAGE_SIZE)
 
 #include <asm/kmap_types.h>
diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index 45aeaaca9052..81061987ac45 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -18,19 +18,20 @@
 #include <asm/tlbflush.h>
 #include "mm.h"
 
-pte_t *fixmap_page_table;
-
 static inline void set_fixmap_pte(int idx, pte_t pte)
 {
 	unsigned long vaddr = __fix_to_virt(idx);
-	set_pte_ext(fixmap_page_table + idx, pte, 0);
+	pte_t *ptep = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
+
+	set_pte_ext(ptep, pte, 0);
 	local_flush_tlb_kernel_page(vaddr);
 }
 
 static inline pte_t get_fixmap_pte(unsigned long vaddr)
 {
-	unsigned long idx = __virt_to_fix(vaddr);
-	return *(fixmap_page_table + idx);
+	pte_t *ptep = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
+
+	return *ptep;
 }
 
 void *kmap(struct page *page)
@@ -84,7 +85,7 @@ void *kmap_atomic(struct page *page)
 	 * With debugging enabled, kunmap_atomic forces that entry to 0.
 	 * Make sure it was indeed properly unmapped.
 	 */
-	BUG_ON(!pte_none(*(fixmap_page_table + idx)));
+	BUG_ON(!pte_none(get_fixmap_pte(vaddr)));
 #endif
 	/*
 	 * When debugging is off, kunmap_atomic leaves the previous mapping
@@ -134,7 +135,7 @@ void *kmap_atomic_pfn(unsigned long pfn)
 	idx = type + KM_TYPE_NR * smp_processor_id();
 	vaddr = __fix_to_virt(idx);
 #ifdef CONFIG_DEBUG_HIGHMEM
-	BUG_ON(!pte_none(*(fixmap_page_table + idx)));
+	BUG_ON(!pte_none(get_fixmap_pte(vaddr)));
 #endif
 	set_fixmap_pte(idx, pfn_pte(pfn, kmap_prot));
 
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 8348ed6b2efe..7fa0966cd15f 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1326,10 +1326,10 @@ static void __init kmap_init(void)
 #ifdef CONFIG_HIGHMEM
 	pkmap_page_table = early_pte_alloc(pmd_off_k(PKMAP_BASE),
 		PKMAP_BASE, _PAGE_KERNEL_TABLE);
-
-	fixmap_page_table = early_pte_alloc(pmd_off_k(FIXADDR_START),
-		FIXADDR_START, _PAGE_KERNEL_TABLE);
 #endif
+
+	early_pte_alloc(pmd_off_k(FIXADDR_START), FIXADDR_START,
+			_PAGE_KERNEL_TABLE);
 }
 
 static void __init map_lowmem(void)
-- 
1.9.1

[PATCH v6 3/8] arm: fixmap: implement __set_fixmap()

[Kees Cook]

This is used from set_fixmap() and clear_fixmap() via asm-generic/fixmap.h.
Also makes sure that the fixmap allocation fits into the expected range.

Based on patch by Rabin Vincent.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Rabin Vincent <rabin@rab.in>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/include/asm/fixmap.h |  2 ++
 arch/arm/mm/mmu.c             | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index d984ca69ce19..714606f70425 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -14,6 +14,8 @@ enum fixed_addresses {
 	__end_of_fixed_addresses
 };
 
+void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot);
+
 #include <asm-generic/fixmap.h>
 
 #endif
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 7fa0966cd15f..bdf5c94f7c36 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -22,6 +22,7 @@
 #include <asm/cputype.h>
 #include <asm/sections.h>
 #include <asm/cachetype.h>
+#include <asm/fixmap.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
 #include <asm/smp_plat.h>
@@ -393,6 +394,29 @@ SET_MEMORY_FN(x, pte_set_x)
 SET_MEMORY_FN(nx, pte_set_nx)
 
 /*
+ * To avoid TLB flush broadcasts, this uses local_flush_tlb_kernel_range().
+ * As a result, this can only be called with preemption disabled, as under
+ * stop_machine().
+ */
+void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
+{
+	unsigned long vaddr = __fix_to_virt(idx);
+	pte_t *pte = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
+
+	/* Make sure fixmap region does not exceed available allocation. */
+	BUILD_BUG_ON(FIXADDR_START + (__end_of_fixed_addresses * PAGE_SIZE) >
+		     FIXADDR_END);
+	BUG_ON(idx >= __end_of_fixed_addresses);
+
+	if (pgprot_val(prot))
+		set_pte_at(NULL, vaddr, pte,
+			pfn_pte(phys >> PAGE_SHIFT, prot));
+	else
+		pte_clear(NULL, vaddr, pte);
+	local_flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
+}
+
+/*
  * Adjust the PMD section entries according to the CPU in use.
  */
 static void __init build_mem_type_table(void)
-- 
1.9.1

[PATCH v6 4/8] arm: use fixmap for text patching when text is RO

[Kees Cook]

From: Rabin Vincent <rabin@rab.in>

Use fixmaps for text patching when the kernel text is read-only,
inspired by x86.  This makes jump labels and kprobes work with the
currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
CONFIG_DEBUG_RODATA options.

Signed-off-by: Rabin Vincent <rabin@rab.in>
[kees: fixed up for merge with "arm: use generic fixmap.h"]
[kees: added parse acquire/release annotations to pass C=1 builds]
[kees: always use stop_machine to keep TLB flushing local]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/include/asm/fixmap.h |  4 ++
 arch/arm/kernel/jump_label.c  |  2 +-
 arch/arm/kernel/patch.c       | 92 ++++++++++++++++++++++++++++++++++---------
 arch/arm/kernel/patch.h       | 12 +++++-
 4 files changed, 89 insertions(+), 21 deletions(-)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 714606f70425..0415eae1df27 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -11,6 +11,10 @@ enum fixed_addresses {
 	FIX_KMAP_BEGIN,
 	FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1,
 
+	/* Support writing RO kernel text via kprobes, jump labels, etc. */
+	FIX_TEXT_POKE0,
+	FIX_TEXT_POKE1,
+
 	__end_of_fixed_addresses
 };
 
diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
index 4ce4f789446d..afeeb9ea6f43 100644
--- a/arch/arm/kernel/jump_label.c
+++ b/arch/arm/kernel/jump_label.c
@@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
 		insn = arm_gen_nop();
 
 	if (is_static)
-		__patch_text(addr, insn);
+		__patch_text_early(addr, insn);
 	else
 		patch_text(addr, insn);
 }
diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
index 07314af47733..5038960e3c55 100644
--- a/arch/arm/kernel/patch.c
+++ b/arch/arm/kernel/patch.c
@@ -1,8 +1,11 @@
 #include <linux/kernel.h>
+#include <linux/spinlock.h>
 #include <linux/kprobes.h>
+#include <linux/mm.h>
 #include <linux/stop_machine.h>
 
 #include <asm/cacheflush.h>
+#include <asm/fixmap.h>
 #include <asm/smp_plat.h>
 #include <asm/opcodes.h>
 
@@ -13,21 +16,77 @@ struct patch {
 	unsigned int insn;
 };
 
-void __kprobes __patch_text(void *addr, unsigned int insn)
+static DEFINE_SPINLOCK(patch_lock);
+
+static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
+	__acquires(&patch_lock)
+{
+	unsigned int uintaddr = (uintptr_t) addr;
+	bool module = !core_kernel_text(uintaddr);
+	struct page *page;
+
+	if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
+		page = vmalloc_to_page(addr);
+	else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
+		page = virt_to_page(addr);
+	else
+		return addr;
+
+	if (flags)
+		spin_lock_irqsave(&patch_lock, *flags);
+	else
+		__acquire(&patch_lock);
+
+	set_fixmap(fixmap, page_to_phys(page));
+
+	return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
+}
+
+static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
+	__releases(&patch_lock)
+{
+	clear_fixmap(fixmap);
+
+	if (flags)
+		spin_unlock_irqrestore(&patch_lock, *flags);
+	else
+		__release(&patch_lock);
+}
+
+void __kprobes __patch_text_real(void *addr, unsigned int insn, bool remap)
 {
 	bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
+	unsigned int uintaddr = (uintptr_t) addr;
+	bool twopage = false;
+	unsigned long flags;
+	void *waddr = addr;
 	int size;
 
+	if (remap)
+		waddr = patch_map(addr, FIX_TEXT_POKE0, &flags);
+	else
+		__acquire(&patch_lock);
+
 	if (thumb2 && __opcode_is_thumb16(insn)) {
-		*(u16 *)addr = __opcode_to_mem_thumb16(insn);
+		*(u16 *)waddr = __opcode_to_mem_thumb16(insn);
 		size = sizeof(u16);
-	} else if (thumb2 && ((uintptr_t)addr & 2)) {
+	} else if (thumb2 && (uintaddr & 2)) {
 		u16 first = __opcode_thumb32_first(insn);
 		u16 second = __opcode_thumb32_second(insn);
-		u16 *addrh = addr;
+		u16 *addrh0 = waddr;
+		u16 *addrh1 = waddr + 2;
+
+		twopage = (uintaddr & ~PAGE_MASK) == PAGE_SIZE - 2;
+		if (twopage && remap)
+			addrh1 = patch_map(addr + 2, FIX_TEXT_POKE1, NULL);
+
+		*addrh0 = __opcode_to_mem_thumb16(first);
+		*addrh1 = __opcode_to_mem_thumb16(second);
 
-		addrh[0] = __opcode_to_mem_thumb16(first);
-		addrh[1] = __opcode_to_mem_thumb16(second);
+		if (twopage && addrh1 != addr + 2) {
+			flush_kernel_vmap_range(addrh1, 2);
+			patch_unmap(FIX_TEXT_POKE1, NULL);
+		}
 
 		size = sizeof(u32);
 	} else {
@@ -36,10 +95,16 @@ void __kprobes __patch_text(void *addr, unsigned int insn)
 		else
 			insn = __opcode_to_mem_arm(insn);
 
-		*(u32 *)addr = insn;
+		*(u32 *)waddr = insn;
 		size = sizeof(u32);
 	}
 
+	if (waddr != addr) {
+		flush_kernel_vmap_range(waddr, twopage ? size / 2 : size);
+		patch_unmap(FIX_TEXT_POKE0, &flags);
+	} else
+		__release(&patch_lock);
+
 	flush_icache_range((uintptr_t)(addr),
 			   (uintptr_t)(addr) + size);
 }
@@ -60,16 +125,5 @@ void __kprobes patch_text(void *addr, unsigned int insn)
 		.insn = insn,
 	};
 
-	if (cache_ops_need_broadcast()) {
-		stop_machine(patch_text_stop_machine, &patch, cpu_online_mask);
-	} else {
-		bool straddles_word = IS_ENABLED(CONFIG_THUMB2_KERNEL)
-				      && __opcode_is_thumb32(insn)
-				      && ((uintptr_t)addr & 2);
-
-		if (straddles_word)
-			stop_machine(patch_text_stop_machine, &patch, NULL);
-		else
-			__patch_text(addr, insn);
-	}
+	stop_machine(patch_text_stop_machine, &patch, NULL);
 }
diff --git a/arch/arm/kernel/patch.h b/arch/arm/kernel/patch.h
index b4731f2dac38..77e054c2f6cd 100644
--- a/arch/arm/kernel/patch.h
+++ b/arch/arm/kernel/patch.h
@@ -2,6 +2,16 @@
 #define _ARM_KERNEL_PATCH_H
 
 void patch_text(void *addr, unsigned int insn);
-void __patch_text(void *addr, unsigned int insn);
+void __patch_text_real(void *addr, unsigned int insn, bool remap);
+
+static inline void __patch_text(void *addr, unsigned int insn)
+{
+	__patch_text_real(addr, insn, true);
+}
+
+static inline void __patch_text_early(void *addr, unsigned int insn)
+{
+	__patch_text_real(addr, insn, false);
+}
 
 #endif
-- 
1.9.1

[PATCH v6 5/8] ARM: kexec: Make .text R/W in machine_kexec

[Kees Cook]

From: Nikolay Borisov <Nikolay.Borisov@arm.com>

With the introduction of Kees Cook's patch to make the kernel .text
read-only the existing method by which kexec works got broken since it
directly pokes some values in the template code, which resides in the
.text section.

The current patch changes the way those values are inserted so that poking
.text section occurs only in machine_kexec (e.g when we are about to nuke
the old kernel and are beyond the point of return). This allows to use
set_kernel_text_rw() to directly patch the values in the .text section.

I had already sent a patch which achieved this but it was significantly
more complicated, so this is a cleaner/straight-forward approach.

Signed-off-by: Nikolay Borisov <Nikolay.Borisov@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
[kees: collapsed kexec_boot_atags (will.daecon)]
[kees: for bisectability, moved set_kernel_text_rw() to RODATA patch]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/kernel/machine_kexec.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 8cf0996aa1a8..8f75250cbe30 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -29,6 +29,7 @@ extern unsigned long kexec_boot_atags;
 
 static atomic_t waiting_for_crash_ipi;
 
+static unsigned long dt_mem;
 /*
  * Provide a dummy crash_notes definition while crash dump arrives to arm.
  * This prevents breakage of crash_notes attribute in kernel/ksysfs.c.
@@ -64,7 +65,7 @@ int machine_kexec_prepare(struct kimage *image)
 			return err;
 
 		if (be32_to_cpu(header) == OF_DT_HEADER)
-			kexec_boot_atags = current_segment->mem;
+			dt_mem = current_segment->mem;
 	}
 	return 0;
 }
@@ -166,9 +167,8 @@ void machine_kexec(struct kimage *image)
 	kexec_start_address = image->start;
 	kexec_indirection_page = page_list;
 	kexec_mach_type = machine_arch_type;
-	if (!kexec_boot_atags)
-		kexec_boot_atags = image->start - KEXEC_ARM_ZIMAGE_OFFSET + KEXEC_ARM_ATAGS_OFFSET;
-
+	kexec_boot_atags = dt_mem ?: image->start - KEXEC_ARM_ZIMAGE_OFFSET
+				     + KEXEC_ARM_ATAGS_OFFSET;
 
 	/* copy our kernel relocation code to the control code page */
 	reboot_entry = fncpy(reboot_code_buffer,
-- 
1.9.1

[PATCH v6 6/8] arm: kgdb: Handle read-only text / modules

[Kees Cook]

From: Doug Anderson <dianders@chromium.org>

Handle the case where someone has set the text segment of the kernel
as read-only by using the newly introduced "patch" mechanism.

Signed-off-by: Doug Anderson <dianders@chromium.org>
[kees: switched structure size check to BUILD_BUG_ON (sboyd)]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/kernel/Makefile |  2 +-
 arch/arm/kernel/kgdb.c   | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 38ddd9f83d0e..70b730766330 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -67,7 +67,7 @@ test-kprobes-objs		+= kprobes-test-arm.o
 endif
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
 obj-$(CONFIG_ARM_THUMBEE)	+= thumbee.o
-obj-$(CONFIG_KGDB)		+= kgdb.o
+obj-$(CONFIG_KGDB)		+= kgdb.o patch.o
 obj-$(CONFIG_ARM_UNWIND)	+= unwind.o
 obj-$(CONFIG_HAVE_TCM)		+= tcm.o
 obj-$(CONFIG_OF)		+= devtree.o
diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
index a74b53c1b7df..07db2f8a1b45 100644
--- a/arch/arm/kernel/kgdb.c
+++ b/arch/arm/kernel/kgdb.c
@@ -12,8 +12,12 @@
 #include <linux/irq.h>
 #include <linux/kdebug.h>
 #include <linux/kgdb.h>
+#include <linux/uaccess.h>
+
 #include <asm/traps.h>
 
+#include "patch.h"
+
 struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] =
 {
 	{ "r0", 4, offsetof(struct pt_regs, ARM_r0)},
@@ -244,6 +248,31 @@ void kgdb_arch_exit(void)
 	unregister_die_notifier(&kgdb_notifier);
 }
 
+int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
+{
+	int err;
+
+	/* patch_text() only supports int-sized breakpoints */
+	BUILD_BUG_ON(sizeof(int) != BREAK_INSTR_SIZE);
+
+	err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
+				BREAK_INSTR_SIZE);
+	if (err)
+		return err;
+
+	patch_text((void *)bpt->bpt_addr,
+		   *(unsigned int *)arch_kgdb_ops.gdb_bpt_instr);
+
+	return err;
+}
+
+int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
+{
+	patch_text((void *)bpt->bpt_addr, *(unsigned int *)bpt->saved_instr);
+
+	return 0;
+}
+
 /*
  * Register our undef instruction hooks with ARM undef core.
  * We regsiter a hook specifically looking for the KGB break inst
-- 
1.9.1

[PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable

[Kees Cook]

Adds CONFIG_ARM_KERNMEM_PERMS to separate the kernel memory regions
into section-sized areas that can have different permisions. Performs
the NX permission changes during free_initmem, so that init memory can be
reclaimed.

This uses section size instead of PMD size to reduce memory lost to
padding on non-LPAE systems.

Based on work by Brad Spengler, Larry Bassel, and Laura Abbott.

Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <lauraa@codeaurora.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/kernel/vmlinux.lds.S |  17 +++++++
 arch/arm/mm/Kconfig           |   9 ++++
 arch/arm/mm/init.c            | 101 +++++++++++++++++++++++++++++++++++++++++-
 arch/arm/mm/mmu.c             |  13 +++++-
 4 files changed, 138 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 6f57cb94367f..a3d07ca2bbb4 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -8,6 +8,9 @@
 #include <asm/thread_info.h>
 #include <asm/memory.h>
 #include <asm/page.h>
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+#include <asm/pgtable.h>
+#endif
 	
 #define PROC_INFO							\
 	. = ALIGN(4);							\
@@ -90,6 +93,11 @@ SECTIONS
 		_text = .;
 		HEAD_TEXT
 	}
+
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+	. = ALIGN(1<<SECTION_SHIFT);
+#endif
+
 	.text : {			/* Real text segment		*/
 		_stext = .;		/* Text and read-only data	*/
 			__exception_text_start = .;
@@ -145,7 +153,11 @@ SECTIONS
 	_etext = .;			/* End of text and rodata section */
 
 #ifndef CONFIG_XIP_KERNEL
+# ifdef CONFIG_ARM_KERNMEM_PERMS
+	. = ALIGN(1<<SECTION_SHIFT);
+# else
 	. = ALIGN(PAGE_SIZE);
+# endif
 	__init_begin = .;
 #endif
 	/*
@@ -220,7 +232,12 @@ SECTIONS
 	. = PAGE_OFFSET + TEXT_OFFSET;
 #else
 	__init_end = .;
+
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+	. = ALIGN(1<<SECTION_SHIFT);
+#else
 	. = ALIGN(THREAD_SIZE);
+#endif
 	__data_loc = .;
 #endif
 
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index ae69809a9e47..7a0756df91a2 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -1008,3 +1008,12 @@ config ARCH_SUPPORTS_BIG_ENDIAN
 	help
 	  This option specifies the architecture can support big endian
 	  operation.
+
+config ARM_KERNMEM_PERMS
+	bool "Restrict kernel memory permissions"
+	help
+	  If this is set, kernel memory other than kernel text (and rodata)
+	  will be made non-executable. The tradeoff is that each region is
+	  padded to section-size (1MiB) boundaries (because their permissions
+	  are different and splitting the 1M pages into 4K ones causes TLB
+	  performance problems), wasting memory.
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index ad82c05bfc3a..e6bfe76b2f59 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -29,6 +29,7 @@
 #include <asm/prom.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
+#include <asm/system_info.h>
 #include <asm/tlb.h>
 #include <asm/fixmap.h>
 
@@ -615,7 +616,99 @@ void __init mem_init(void)
 	}
 }
 
-void free_initmem(void)
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+struct section_perm {
+	unsigned long start;
+	unsigned long end;
+	pmdval_t mask;
+	pmdval_t prot;
+};
+
+struct section_perm nx_perms[] = {
+	/* Make pages tables, etc before _stext RW (set NX). */
+	{
+		.start	= PAGE_OFFSET,
+		.end	= (unsigned long)_stext,
+		.mask	= ~PMD_SECT_XN,
+		.prot	= PMD_SECT_XN,
+	},
+	/* Make init RW (set NX). */
+	{
+		.start	= (unsigned long)__init_begin,
+		.end	= (unsigned long)_sdata,
+		.mask	= ~PMD_SECT_XN,
+		.prot	= PMD_SECT_XN,
+	},
+};
+
+/*
+ * Updates section permissions only for the current mm (sections are
+ * copied into each mm). During startup, this is the init_mm. Is only
+ * safe to be called with preemption disabled, as under stop_machine().
+ */
+static inline void section_update(unsigned long addr, pmdval_t mask,
+				  pmdval_t prot)
+{
+	struct mm_struct *mm;
+	pmd_t *pmd;
+
+	mm = current->active_mm;
+	pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr);
+
+#ifdef CONFIG_ARM_LPAE
+	pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
+#else
+	if (addr & SECTION_SIZE)
+		pmd[1] = __pmd((pmd_val(pmd[1]) & mask) | prot);
+	else
+		pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
+#endif
+	flush_pmd_entry(pmd);
+	local_flush_tlb_kernel_range(addr, addr + SECTION_SIZE);
+}
+
+/* Make sure extended page tables are in use. */
+static inline bool arch_has_strict_perms(void)
+{
+	if (cpu_architecture() < CPU_ARCH_ARMv6)
+		return false;
+
+	return !!(get_cr() & CR_XP);
+}
+
+#define set_section_perms(perms, field)	{				\
+	size_t i;							\
+	unsigned long addr;						\
+									\
+	if (!arch_has_strict_perms())					\
+		return;							\
+									\
+	for (i = 0; i < ARRAY_SIZE(perms); i++) {			\
+		if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) ||	\
+		    !IS_ALIGNED(perms[i].end, SECTION_SIZE)) {		\
+			pr_err("BUG: section %lx-%lx not aligned to %lx\n", \
+				perms[i].start, perms[i].end,		\
+				SECTION_SIZE);				\
+			continue;					\
+		}							\
+									\
+		for (addr = perms[i].start;				\
+		     addr < perms[i].end;				\
+		     addr += SECTION_SIZE)				\
+			section_update(addr, perms[i].mask,		\
+				       perms[i].field);			\
+	}								\
+}
+
+static inline void fix_kernmem_perms(void)
+{
+	set_section_perms(nx_perms, prot);
+}
+#else
+static inline void fix_kernmem_perms(void) { }
+#endif /* CONFIG_ARM_KERNMEM_PERMS */
+
+void free_tcmmem(void)
 {
 #ifdef CONFIG_HAVE_TCM
 	extern char __tcm_start, __tcm_end;
@@ -623,6 +716,12 @@ void free_initmem(void)
 	poison_init_mem(&__tcm_start, &__tcm_end - &__tcm_start);
 	free_reserved_area(&__tcm_start, &__tcm_end, -1, "TCM link");
 #endif
+}
+
+void free_initmem(void)
+{
+	fix_kernmem_perms();
+	free_tcmmem();
 
 	poison_init_mem(__init_begin, __init_end - __init_begin);
 	if (!machine_is_integrator() && !machine_is_cintegrator())
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index bdf5c94f7c36..2e93388c6d92 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1373,13 +1373,24 @@ static void __init map_lowmem(void)
 		if (start >= end)
 			break;
 
-		if (end < kernel_x_start || start >= kernel_x_end) {
+		if (end < kernel_x_start) {
 			map.pfn = __phys_to_pfn(start);
 			map.virtual = __phys_to_virt(start);
 			map.length = end - start;
 			map.type = MT_MEMORY_RWX;
 
 			create_mapping(&map);
+		} else if (start >= kernel_x_end) {
+			map.pfn = __phys_to_pfn(start);
+			map.virtual = __phys_to_virt(start);
+			map.length = end - start;
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+			map.type = MT_MEMORY_RW;
+#else
+			map.type = MT_MEMORY_RWX;
+#endif
+
+			create_mapping(&map);
 		} else {
 			/* This better cover the entire kernel */
 			if (start < kernel_x_start) {
-- 
1.9.1

[PATCH v6 8/8] ARM: mm: allow text and rodata sections to be read-only

[Kees Cook]

This introduces CONFIG_DEBUG_RODATA, making kernel text and rodata
read-only. Additionally, this splits rodata from text so that rodata can
also be NX, which may lead to wasted memory when aligning to SECTION_SIZE.
The read-only areas are made writable during ftrace updates and kexec.

Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <lauraa@codeaurora.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/include/asm/cacheflush.h | 10 ++++++++
 arch/arm/kernel/ftrace.c          | 19 ++++++++++++++++
 arch/arm/kernel/machine_kexec.c   |  1 +
 arch/arm/kernel/vmlinux.lds.S     |  3 +++
 arch/arm/mm/Kconfig               | 12 ++++++++++
 arch/arm/mm/init.c                | 48 ++++++++++++++++++++++++++++++++++++++-
 6 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index 79ecb4f34ffb..9108292edcb5 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -486,6 +486,16 @@ int set_memory_rw(unsigned long addr, int numpages);
 int set_memory_x(unsigned long addr, int numpages);
 int set_memory_nx(unsigned long addr, int numpages);
 
+#ifdef CONFIG_DEBUG_RODATA
+void mark_rodata_ro(void);
+void set_kernel_text_rw(void);
+void set_kernel_text_ro(void);
+#else
+static inline void set_kernel_text_rw(void) { }
+static inline void set_kernel_text_ro(void) { }
+#endif
+
 void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
 			     void *kaddr, unsigned long len);
+
 #endif
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index af9a8a927a4e..b8c75e45a950 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -15,6 +15,7 @@
 #include <linux/ftrace.h>
 #include <linux/uaccess.h>
 #include <linux/module.h>
+#include <linux/stop_machine.h>
 
 #include <asm/cacheflush.h>
 #include <asm/opcodes.h>
@@ -35,6 +36,22 @@
 
 #define	OLD_NOP		0xe1a00000	/* mov r0, r0 */
 
+static int __ftrace_modify_code(void *data)
+{
+	int *command = data;
+
+	set_kernel_text_rw();
+	ftrace_modify_all_code(*command);
+	set_kernel_text_ro();
+
+	return 0;
+}
+
+void arch_ftrace_update_code(int command)
+{
+	stop_machine(__ftrace_modify_code, &command, NULL);
+}
+
 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
 {
 	return rec->arch.old_mcount ? OLD_NOP : NOP;
@@ -73,6 +90,8 @@ int ftrace_arch_code_modify_prepare(void)
 int ftrace_arch_code_modify_post_process(void)
 {
 	set_all_modules_text_ro();
+	/* Make sure any TLB misses during machine stop are cleared. */
+	flush_tlb_all();
 	return 0;
 }
 
diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 8f75250cbe30..4423a565ef6f 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -164,6 +164,7 @@ void machine_kexec(struct kimage *image)
 	reboot_code_buffer = page_address(image->control_code_page);
 
 	/* Prepare parameters for reboot_code_buffer*/
+	set_kernel_text_rw();
 	kexec_start_address = image->start;
 	kexec_indirection_page = page_list;
 	kexec_mach_type = machine_arch_type;
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index a3d07ca2bbb4..542e58919bd9 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -120,6 +120,9 @@ SECTIONS
 			ARM_CPU_KEEP(PROC_INFO)
 	}
 
+#ifdef CONFIG_DEBUG_RODATA
+	. = ALIGN(1<<SECTION_SHIFT);
+#endif
 	RO_DATA(PAGE_SIZE)
 
 	. = ALIGN(4);
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 7a0756df91a2..c9cd9c5bf1e1 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -1017,3 +1017,15 @@ config ARM_KERNMEM_PERMS
 	  padded to section-size (1MiB) boundaries (because their permissions
 	  are different and splitting the 1M pages into 4K ones causes TLB
 	  performance problems), wasting memory.
+
+config DEBUG_RODATA
+	bool "Make kernel text and rodata read-only"
+	depends on ARM_KERNMEM_PERMS
+	default y
+	help
+	  If this is set, kernel text and rodata will be made read-only. This
+	  is to help catch accidental or malicious attempts to change the
+	  kernel's executable code. Additionally splits rodata from kernel
+	  text so it can be made explicitly non-executable. This creates
+	  another section-size padded region, so it can waste more memory
+	  space while gaining the read-only protections.
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index e6bfe76b2f59..dc2db779cdf4 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -622,9 +622,10 @@ struct section_perm {
 	unsigned long end;
 	pmdval_t mask;
 	pmdval_t prot;
+	pmdval_t clear;
 };
 
-struct section_perm nx_perms[] = {
+static struct section_perm nx_perms[] = {
 	/* Make pages tables, etc before _stext RW (set NX). */
 	{
 		.start	= PAGE_OFFSET,
@@ -639,8 +640,35 @@ struct section_perm nx_perms[] = {
 		.mask	= ~PMD_SECT_XN,
 		.prot	= PMD_SECT_XN,
 	},
+#ifdef CONFIG_DEBUG_RODATA
+	/* Make rodata NX (set RO in ro_perms below). */
+	{
+		.start  = (unsigned long)__start_rodata,
+		.end    = (unsigned long)__init_begin,
+		.mask   = ~PMD_SECT_XN,
+		.prot   = PMD_SECT_XN,
+	},
+#endif
 };
 
+#ifdef CONFIG_DEBUG_RODATA
+static struct section_perm ro_perms[] = {
+	/* Make kernel code and rodata RX (set RO). */
+	{
+		.start  = (unsigned long)_stext,
+		.end    = (unsigned long)__init_begin,
+#ifdef CONFIG_ARM_LPAE
+		.mask   = ~PMD_SECT_RDONLY,
+		.prot   = PMD_SECT_RDONLY,
+#else
+		.mask   = ~(PMD_SECT_APX | PMD_SECT_AP_WRITE),
+		.prot   = PMD_SECT_APX | PMD_SECT_AP_WRITE,
+		.clear  = PMD_SECT_AP_WRITE,
+#endif
+	},
+};
+#endif
+
 /*
  * Updates section permissions only for the current mm (sections are
  * copied into each mm). During startup, this is the init_mm. Is only
@@ -704,6 +732,24 @@ static inline void fix_kernmem_perms(void)
 {
 	set_section_perms(nx_perms, prot);
 }
+
+#ifdef CONFIG_DEBUG_RODATA
+void mark_rodata_ro(void)
+{
+	set_section_perms(ro_perms, prot);
+}
+
+void set_kernel_text_rw(void)
+{
+	set_section_perms(ro_perms, clear);
+}
+
+void set_kernel_text_ro(void)
+{
+	set_section_perms(ro_perms, prot);
+}
+#endif /* CONFIG_DEBUG_RODATA */
+
 #else
 static inline void fix_kernmem_perms(void) { }
 #endif /* CONFIG_ARM_KERNMEM_PERMS */
-- 
1.9.1

Re: [PATCH v6 0/8] arm: support CONFIG_RODATA

[Kees Cook]

On Thu, Sep 18, 2014 at 12:19 PM, Kees Cook <keescook@chromium.org> wrote:
> This is a series of patches to support CONFIG_RODATA on ARM, so that
> the kernel text is RO, and non-text sections default to NX. To support
> on-the-fly kernel text patching (via ftrace, kprobes, etc), fixmap
> support has been finalized based on several versions of various patches
> that are floating around on the mailing list. This series attempts to
> include the least intrusive version, so that others can build on it for
> future fixmap work.
>
> The series has been heavily tested, and appears to be working correctly:
>
> With CONFIG_ARM_PTDUMP, expected page table permissions are seen in
> /sys/kernel/debug/kernel_page_tables.
>
> Using CONFIG_LKDTM, the kernel now correctly detects bad accesses for
> for the following lkdtm tests via /sys/kernel/debug/provoke-crash/DIRECT:
>         EXEC_DATA
>         WRITE_RO
>         WRITE_KERN
>
> ftrace works:
>         CONFIG_FTRACE_STARTUP_TEST passes
>         Enabling tracing works:
>                 echo function > /sys/kernel/debug/tracing/current_tracer
> kprobes works:
>         CONFIG_ARM_KPROBES_TEST passes
>
> kexec works:
>         kexec will load and start a new kernel
>
> Built with and without CONFIG_HIGHMEM, CONFIG_HIGHMEM_DEBUG, and
> CONFIG_NR_CPUS=32.
>
> Thanks to everyone who has been testing this series and working on its
> various pieces!
>
> Hopefully this should address Will's last concerns. :)
>
> Thanks!
>
> -Kees
>
> v6:
> - always run patch_text under stop_machine (will.deacon)
> - document set_fixmap's TLB flushing situation (will.deacon)

Hi Will,

Does this version look good to you? Should I turn it into a pull request?

Thanks!

-Kees

>
> v5:
> - clean up #includes in mmu.c (will.deacon)
> - optimize get_cr() test (will.deacon)
> - created free_tcmmem to avoid excessive #ifdefs (will.deacon)
> - explicitly test irqs_disabled in set_fixmap (will.deacon)
>
> v4:
> - expanded fixmap to 3MB to support 32 CPUs (robh)
> - corrected pmd-finding via vaddr instead of FIXMAP_START (robh)
> - switched structure size test to BUILD_BUG_ON (sboyd)
> - added locking annotations to keep sparse happy (sboyd)
> - adding missing "static" declarations noticed by sparse
> - reorganized fixmap portion of patches
>
> v3:
> - more cleanups in switch to generic fixmap (lauraa, robh)
> - fixed kexec merge hunk glitch (will.deacon)
> - added tested-by tags where appropriate from v2 testing
>
> v2:
> - fix typo in kexec merge (buildbot)
> - flip index order for highmem pte access (lauraa)
> - added kgdb updates (dianders)
>



-- 
Kees Cook
Chrome OS Security

Re: [PATCH v6 0/8] arm: support CONFIG_RODATA

[Will Deacon]

On Fri, Sep 26, 2014 at 06:58:05AM +0100, Kees Cook wrote:
> On Thu, Sep 18, 2014 at 12:19 PM, Kees Cook <keescook@chromium.org> wrote:
> > This is a series of patches to support CONFIG_RODATA on ARM, so that
> > the kernel text is RO, and non-text sections default to NX. To support
> > on-the-fly kernel text patching (via ftrace, kprobes, etc), fixmap
> > support has been finalized based on several versions of various patches
> > that are floating around on the mailing list. This series attempts to
> > include the least intrusive version, so that others can build on it for
> > future fixmap work.
> >
> > The series has been heavily tested, and appears to be working correctly:
> >
> > With CONFIG_ARM_PTDUMP, expected page table permissions are seen in
> > /sys/kernel/debug/kernel_page_tables.
> >
> > Using CONFIG_LKDTM, the kernel now correctly detects bad accesses for
> > for the following lkdtm tests via /sys/kernel/debug/provoke-crash/DIRECT:
> >         EXEC_DATA
> >         WRITE_RO
> >         WRITE_KERN
> >
> > ftrace works:
> >         CONFIG_FTRACE_STARTUP_TEST passes
> >         Enabling tracing works:
> >                 echo function > /sys/kernel/debug/tracing/current_tracer
> > kprobes works:
> >         CONFIG_ARM_KPROBES_TEST passes
> >
> > kexec works:
> >         kexec will load and start a new kernel
> >
> > Built with and without CONFIG_HIGHMEM, CONFIG_HIGHMEM_DEBUG, and
> > CONFIG_NR_CPUS=32.
> >
> > Thanks to everyone who has been testing this series and working on its
> > various pieces!
> >
> > Hopefully this should address Will's last concerns. :)
> >
> > Thanks!
> >
> > -Kees
> >
> > v6:
> > - always run patch_text under stop_machine (will.deacon)
> > - document set_fixmap's TLB flushing situation (will.deacon)
> 
> Hi Will,
> 
> Does this version look good to you? Should I turn it into a pull request?

The TLB flushing bits look sensible now, but the locking in __set_fixmap is
still pretty horrible (x86 just uses a mutex, not sure why we need to be
different). Still, it's Russell's call.

Will

Re: [PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable

[Russell King - ARM Linux]

On Thu, Sep 18, 2014 at 12:19:08PM -0700, Kees Cook wrote:
> @@ -1373,13 +1373,24 @@ static void __init map_lowmem(void)
>  		if (start >= end)
>  			break;
>  
> -		if (end < kernel_x_start || start >= kernel_x_end) {
> +		if (end < kernel_x_start) {
>  			map.pfn = __phys_to_pfn(start);
>  			map.virtual = __phys_to_virt(start);
>  			map.length = end - start;
>  			map.type = MT_MEMORY_RWX;
>  
>  			create_mapping(&map);
> +		} else if (start >= kernel_x_end) {
> +			map.pfn = __phys_to_pfn(start);
> +			map.virtual = __phys_to_virt(start);
> +			map.length = end - start;
> +#ifdef CONFIG_ARM_KERNMEM_PERMS
> +			map.type = MT_MEMORY_RW;
> +#else
> +			map.type = MT_MEMORY_RWX;
> +#endif
> +
> +			create_mapping(&map);


I'm looking at this, and wondering two things.  Firstly, why isn't it
MT_MEMORY_RW in the first place.  Secondly, why do you need to make
this depend on CONFIG_ARM_KERNMEM_PERMS at all?

I think the first is an oversight by me (and is a case which never came
up in my testing, because most of my platforms don't have segmented
memory layouts.)

The second I think is not necessary - the memory region being considered
is not part of the kernel at all, and so should not be executable in any
shape or form.

-- 
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.

Re: [PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable

[Kees Cook]

On Fri, Sep 26, 2014 at 4:42 AM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Thu, Sep 18, 2014 at 12:19:08PM -0700, Kees Cook wrote:
>> @@ -1373,13 +1373,24 @@ static void __init map_lowmem(void)
>>               if (start >= end)
>>                       break;
>>
>> -             if (end < kernel_x_start || start >= kernel_x_end) {
>> +             if (end < kernel_x_start) {
>>                       map.pfn = __phys_to_pfn(start);
>>                       map.virtual = __phys_to_virt(start);
>>                       map.length = end - start;
>>                       map.type = MT_MEMORY_RWX;
>>
>>                       create_mapping(&map);
>> +             } else if (start >= kernel_x_end) {
>> +                     map.pfn = __phys_to_pfn(start);
>> +                     map.virtual = __phys_to_virt(start);
>> +                     map.length = end - start;
>> +#ifdef CONFIG_ARM_KERNMEM_PERMS
>> +                     map.type = MT_MEMORY_RW;
>> +#else
>> +                     map.type = MT_MEMORY_RWX;
>> +#endif
>> +
>> +                     create_mapping(&map);
>
>
> I'm looking at this, and wondering two things.  Firstly, why isn't it
> MT_MEMORY_RW in the first place.  Secondly, why do you need to make
> this depend on CONFIG_ARM_KERNMEM_PERMS at all?
>
> I think the first is an oversight by me (and is a case which never came
> up in my testing, because most of my platforms don't have segmented
> memory layouts.)
>
> The second I think is not necessary - the memory region being considered
> is not part of the kernel at all, and so should not be executable in any
> shape or form.

I'm happy to change this. My original intent was to make layout for
builds without CONFIG_ARM_KERNMEM_PERMS identical to what was there
before, so I took this step to make sure.

I will drop the #ifdef and respin. Does the rest look ok? Shall I send
a pull request?

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security

Re: [PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable

[Russell King - ARM Linux]

On Fri, Sep 26, 2014 at 09:43:12AM -0700, Kees Cook wrote:
> On Fri, Sep 26, 2014 at 4:42 AM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > On Thu, Sep 18, 2014 at 12:19:08PM -0700, Kees Cook wrote:
> >> @@ -1373,13 +1373,24 @@ static void __init map_lowmem(void)
> >>               if (start >= end)
> >>                       break;
> >>
> >> -             if (end < kernel_x_start || start >= kernel_x_end) {
> >> +             if (end < kernel_x_start) {
> >>                       map.pfn = __phys_to_pfn(start);
> >>                       map.virtual = __phys_to_virt(start);
> >>                       map.length = end - start;
> >>                       map.type = MT_MEMORY_RWX;
> >>
> >>                       create_mapping(&map);
> >> +             } else if (start >= kernel_x_end) {
> >> +                     map.pfn = __phys_to_pfn(start);
> >> +                     map.virtual = __phys_to_virt(start);
> >> +                     map.length = end - start;
> >> +#ifdef CONFIG_ARM_KERNMEM_PERMS
> >> +                     map.type = MT_MEMORY_RW;
> >> +#else
> >> +                     map.type = MT_MEMORY_RWX;
> >> +#endif
> >> +
> >> +                     create_mapping(&map);
> >
> >
> > I'm looking at this, and wondering two things.  Firstly, why isn't it
> > MT_MEMORY_RW in the first place.  Secondly, why do you need to make
> > this depend on CONFIG_ARM_KERNMEM_PERMS at all?
> >
> > I think the first is an oversight by me (and is a case which never came
> > up in my testing, because most of my platforms don't have segmented
> > memory layouts.)
> >
> > The second I think is not necessary - the memory region being considered
> > is not part of the kernel at all, and so should not be executable in any
> > shape or form.
> 
> I'm happy to change this. My original intent was to make layout for
> builds without CONFIG_ARM_KERNMEM_PERMS identical to what was there
> before, so I took this step to make sure.
> 
> I will drop the #ifdef and respin. Does the rest look ok? Shall I send
> a pull request?

I think all you need to is change that MT_MEMORY_RWX to be MT_MEMORY_RW.

However, I think I would also like to see the kernel text being read-only
as soon as possible - so maybe we should also have MT_MEMORY_RX, and
have map_lowmem() use this for the kernel text when we want this level
of protection?

-- 
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.

Re: [PATCH v6 7/8] ARM: mm: allow non-text sections to be non-executable

[Kees Cook]

On Fri, Sep 26, 2014 at 9:59 AM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Fri, Sep 26, 2014 at 09:43:12AM -0700, Kees Cook wrote:
>> On Fri, Sep 26, 2014 at 4:42 AM, Russell King - ARM Linux
>> <linux@arm.linux.org.uk> wrote:
>> > On Thu, Sep 18, 2014 at 12:19:08PM -0700, Kees Cook wrote:
>> >> @@ -1373,13 +1373,24 @@ static void __init map_lowmem(void)
>> >>               if (start >= end)
>> >>                       break;
>> >>
>> >> -             if (end < kernel_x_start || start >= kernel_x_end) {
>> >> +             if (end < kernel_x_start) {
>> >>                       map.pfn = __phys_to_pfn(start);
>> >>                       map.virtual = __phys_to_virt(start);
>> >>                       map.length = end - start;
>> >>                       map.type = MT_MEMORY_RWX;
>> >>
>> >>                       create_mapping(&map);
>> >> +             } else if (start >= kernel_x_end) {
>> >> +                     map.pfn = __phys_to_pfn(start);
>> >> +                     map.virtual = __phys_to_virt(start);
>> >> +                     map.length = end - start;
>> >> +#ifdef CONFIG_ARM_KERNMEM_PERMS
>> >> +                     map.type = MT_MEMORY_RW;
>> >> +#else
>> >> +                     map.type = MT_MEMORY_RWX;
>> >> +#endif
>> >> +
>> >> +                     create_mapping(&map);
>> >
>> >
>> > I'm looking at this, and wondering two things.  Firstly, why isn't it
>> > MT_MEMORY_RW in the first place.  Secondly, why do you need to make
>> > this depend on CONFIG_ARM_KERNMEM_PERMS at all?
>> >
>> > I think the first is an oversight by me (and is a case which never came
>> > up in my testing, because most of my platforms don't have segmented
>> > memory layouts.)
>> >
>> > The second I think is not necessary - the memory region being considered
>> > is not part of the kernel at all, and so should not be executable in any
>> > shape or form.
>>
>> I'm happy to change this. My original intent was to make layout for
>> builds without CONFIG_ARM_KERNMEM_PERMS identical to what was there
>> before, so I took this step to make sure.
>>
>> I will drop the #ifdef and respin. Does the rest look ok? Shall I send
>> a pull request?
>
> I think all you need to is change that MT_MEMORY_RWX to be MT_MEMORY_RW.

Okay, I'll make that change.

> However, I think I would also like to see the kernel text being read-only
> as soon as possible - so maybe we should also have MT_MEMORY_RX, and
> have map_lowmem() use this for the kernel text when we want this level
> of protection?

Well, even if that's done we still need all the fixmap stuff happening
too since so many things like to change the kernel memory. :)

I'd like to start with this series, and then we can improve on it
going forward. This one seems to work and has been tested by a lot of
folks so far, so I'd hate to scrap a major portion and start over. I'd
like to get this landed, and then tweak it as needed. Does that sound
workable?

-Kees

-- 
Kees Cook
Chrome OS Security