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[PATCHv8 resend 1/2] x86/vdso: add mremap hook to vm_special_mapping

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  [PATCHv8 resend 1/2] x86/vdso: add mremap hook to vm_special_mapping Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-05-10 15:50 +0200
    [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-05-10 15:50 +0200

#1398108 — [PATCHv8 resend 1/2] x86/vdso: add mremap hook to vm_special_mapping

Add possibility for userspace 32-bit applications to move
vdso mapping. Previously, when userspace app called
mremap for vdso, in return path it would land on previous
address of vdso page, resulting in segmentation violation.
Now it lands fine and returns to userspace with remapped vdso.
This will also fix context.vdso pointer for 64-bit, which does not
affect the user of vdso after mremap by now, but this may change.

As suggested by Andy, return EINVAL for mremap that splits vdso image.

Renamed and moved text_mapping structure declaration inside
map_vdso, as it used only there and now it complement
vvar_mapping variable.

There is still problem for remapping vdso in glibc applications:
linker relocates addresses for syscalls on vdso page, so
you need to relink with the new addresses. Or the next syscall
through glibc may fail:
  Program received signal SIGSEGV, Segmentation fault.
  #0  0xf7fd9b80 in __kernel_vsyscall ()
  #1  0xf7ec8238 in _exit () from /usr/lib32/libc.so.6

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
---
v8: add WARN_ON_ONCE on current->mm != new_vma->vm_mm
v7: build fix
v6: moved vdso_image_32 check and fixup code into vdso_fix_landing function
    with ifdefs around
v5: as Andy suggested, add a check that new_vma->vm_mm and current->mm are
    the same, also check not only in_ia32_syscall() but image == &vdso_image_32
v4: drop __maybe_unused & use image from mm->context instead vdso_image_32
v3: as Andy suggested, return EINVAL in case of splitting vdso blob on mremap;
    used is_ia32_task instead of ifdefs 
v2: added __maybe_unused for pt_regs in vdso_mremap

 arch/x86/entry/vdso/vma.c | 47 ++++++++++++++++++++++++++++++++++++++++++-----
 include/linux/mm_types.h  |  3 +++
 mm/mmap.c                 | 10 ++++++++++
 3 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 10f704584922..0625b66e5648 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -12,6 +12,7 @@
 #include <linux/random.h>
 #include <linux/elf.h>
 #include <linux/cpu.h>
+#include <linux/ptrace.h>
 #include <asm/pvclock.h>
 #include <asm/vgtod.h>
 #include <asm/proto.h>
@@ -98,10 +99,40 @@ static int vdso_fault(const struct vm_special_mapping *sm,
 	return 0;
 }
 
-static const struct vm_special_mapping text_mapping = {
-	.name = "[vdso]",
-	.fault = vdso_fault,
-};
+static void vdso_fix_landing(const struct vdso_image *image,
+		struct vm_area_struct *new_vma)
+{
+#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
+	if (in_ia32_syscall() && image == &vdso_image_32) {
+		struct pt_regs *regs = current_pt_regs();
+		unsigned long vdso_land = image->sym_int80_landing_pad;
+		unsigned long old_land_addr = vdso_land +
+			(unsigned long)current->mm->context.vdso;
+
+		/* Fixing userspace landing - look at do_fast_syscall_32 */
+		if (regs->ip == old_land_addr)
+			regs->ip = new_vma->vm_start + vdso_land;
+	}
+#endif
+}
+
+static int vdso_mremap(const struct vm_special_mapping *sm,
+		struct vm_area_struct *new_vma)
+{
+	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
+	const struct vdso_image *image = current->mm->context.vdso_image;
+
+	if (image->size != new_size)
+		return -EINVAL;
+
+	if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
+		return -EFAULT;
+
+	vdso_fix_landing(image, new_vma);
+	current->mm->context.vdso = (void __user *)new_vma->vm_start;
+
+	return 0;
+}
 
 static int vvar_fault(const struct vm_special_mapping *sm,
 		      struct vm_area_struct *vma, struct vm_fault *vmf)
@@ -162,6 +193,12 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
 	struct vm_area_struct *vma;
 	unsigned long addr, text_start;
 	int ret = 0;
+
+	static const struct vm_special_mapping vdso_mapping = {
+		.name = "[vdso]",
+		.fault = vdso_fault,
+		.mremap = vdso_mremap,
+	};
 	static const struct vm_special_mapping vvar_mapping = {
 		.name = "[vvar]",
 		.fault = vvar_fault,
@@ -195,7 +232,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
 				       image->size,
 				       VM_READ|VM_EXEC|
 				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
-				       &text_mapping);
+				       &vdso_mapping);
 
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c2d75b4fa86c..4d16ab9287af 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -586,6 +586,9 @@ struct vm_special_mapping {
 	int (*fault)(const struct vm_special_mapping *sm,
 		     struct vm_area_struct *vma,
 		     struct vm_fault *vmf);
+
+	int (*mremap)(const struct vm_special_mapping *sm,
+		     struct vm_area_struct *new_vma);
 };
 
 enum tlb_flush_reason {
diff --git a/mm/mmap.c b/mm/mmap.c
index bd2e1a533bc1..ba71658dd1a1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2930,9 +2930,19 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
 	return ((struct vm_special_mapping *)vma->vm_private_data)->name;
 }
 
+static int special_mapping_mremap(struct vm_area_struct *new_vma)
+{
+	struct vm_special_mapping *sm = new_vma->vm_private_data;
+
+	if (sm->mremap)
+		return sm->mremap(sm, new_vma);
+	return 0;
+}
+
 static const struct vm_operations_struct special_mapping_vmops = {
 	.close = special_mapping_close,
 	.fault = special_mapping_fault,
+	.mremap = special_mapping_mremap,
 	.name = special_mapping_name,
 };
 
-- 
2.8.0

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#1398109 — [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test

Should print on success:
[root@localhost ~]# ./test_mremap_vdso_32
	AT_SYSINFO_EHDR is 0xf773f000
[NOTE]	Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
[OK]
Or segfault if landing was bad (before patches):
[root@localhost ~]# ./test_mremap_vdso_32
	AT_SYSINFO_EHDR is 0xf774f000
[NOTE]	Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
Segmentation fault (core dumped)

Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: linux-kselftest@vger.kernel.org
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
---
v8: run test for x86_64 too;
    removed fixed VDSO_SIZE - check EINVAL mremap return for partial remapping
v5: initial version

 tools/testing/selftests/x86/Makefile           |  2 +-
 tools/testing/selftests/x86/test_mremap_vdso.c | 99 ++++++++++++++++++++++++++
 2 files changed, 100 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/x86/test_mremap_vdso.c

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index b47ebd170690..ba865f2efcce 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -5,7 +5,7 @@ include ../lib.mk
 .PHONY: all all_32 all_64 warn_32bit_failure clean
 
 TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall \
-			check_initial_reg_state sigreturn ldt_gdt iopl
+			check_initial_reg_state sigreturn ldt_gdt iopl test_mremap_vdso
 TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \
 			test_FCMOV test_FCOMI test_FISTTP \
 			vdso_restorer
diff --git a/tools/testing/selftests/x86/test_mremap_vdso.c b/tools/testing/selftests/x86/test_mremap_vdso.c
new file mode 100644
index 000000000000..831e2e0107d9
--- /dev/null
+++ b/tools/testing/selftests/x86/test_mremap_vdso.c
@@ -0,0 +1,99 @@
+/*
+ * 32-bit test to check vdso mremap.
+ *
+ * Copyright (c) 2016 Dmitry Safonov
+ * Suggested-by: Andrew Lutomirski
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+/*
+ * Can be built statically:
+ * gcc -Os -Wall -static -m32 test_mremap_vdso.c
+ */
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+
+#include <sys/mman.h>
+#include <sys/auxv.h>
+#include <sys/syscall.h>
+
+#define PAGE_SIZE	4096
+
+static int try_to_remap(void *vdso_addr, unsigned long size)
+{
+	void *dest_addr, *new_addr;
+
+	dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+	if (dest_addr == MAP_FAILED) {
+		printf("[WARN]\tmmap failed (%d): %m\n", errno);
+		return 0;
+	}
+
+	printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",
+		vdso_addr, (unsigned long)vdso_addr + size,
+		dest_addr, (unsigned long)dest_addr + size);
+	fflush(stdout);
+
+	new_addr = mremap(vdso_addr, size, size,
+			MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
+	if ((unsigned long)new_addr == (unsigned long)-1) {
+		munmap(dest_addr, size);
+		if (errno == EINVAL) {
+			printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");
+			return -1; /* retry with larger */
+		}
+		printf("[FAIL]\tmremap failed (%d): %m\n", errno);
+		return 1;
+	}
+
+	return 0;
+
+}
+
+int main(int argc, char **argv, char **envp)
+{
+	unsigned long auxval;
+	const char *ok_string = "[OK]\n";
+	int ret = -1;
+	unsigned long vdso_size = PAGE_SIZE;
+
+	auxval = getauxval(AT_SYSINFO_EHDR);
+	printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);
+	if (!auxval || auxval == -ENOENT) {
+		printf("[WARN]\tgetauxval failed\n");
+		return 0;
+	}
+
+	/* simpler than parsing ELF header */
+	while(ret < 0) {
+		ret = try_to_remap((void *)auxval, vdso_size);
+		vdso_size += PAGE_SIZE;
+	}
+
+	if (!ret)
+#if defined(__i386__)
+		asm volatile ("int $0x80" : :
+			"a" (__NR_write), "b" (STDOUT_FILENO),
+			"c" (ok_string), "d" (strlen(ok_string)));
+
+	asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
+#else
+		asm volatile ("syscall" : :
+			"a" (__NR_write), "D" (STDOUT_FILENO),
+			"S" (ok_string), "d" (strlen(ok_string)));
+
+	asm volatile ("syscall" : : "a" (__NR_exit), "D" (!!ret));
+#endif
+
+	return 0;
+}
-- 
2.8.0

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