virt_to_phys_user

kernel_module/mmap.c

@@ -74,7 +74,7 @@ static int open(struct inode *inode, struct file *filp)
 
 	pr_info("open\n");
 	info = kmalloc(sizeof(struct mmap_info), GFP_KERNEL);
-	pr_info("virt_to_phys = 0x%llx\n", (unsigned long long)virt_to_phys((void *)info->data));
+	pr_info("virt_to_phys = 0x%llx\n", (unsigned long long)virt_to_phys((void *)info));
 	info->data = (char *)get_zeroed_page(GFP_KERNEL);
 	memcpy(info->data, "asdf", BUFFER_SIZE);
 	filp->private_data = info;

kernel_module/user/common.h

@@ -0,0 +1,74 @@
+#ifndef COMMON_H
+#define COMMON_H
+
+#define _POSIX_C_SOURCE 200809L
+#include <fcntl.h> /* open */
+#include <stdint.h> /* uint64_t  */
+#include <stdlib.h> /* size_t */
+#include <unistd.h> /* pread, sysconf */
+
+typedef struct {
+    uint64_t pfn : 54;
+    unsigned int soft_dirty : 1;
+    unsigned int file_page : 1;
+    unsigned int swapped : 1;
+    unsigned int present : 1;
+} PagemapEntry;
+
+/* Parse the pagemap entry for the given virtual address.
+ *
+ * @param[out] entry      the parsed entry
+ * @param[in]  pagemap_fd file descriptor to an open /proc/pid/pagemap file
+ * @param[in]  vaddr      virtual address to get entry for
+ * @return 0 for success, 1 for failure
+ */
+int pagemap_get_entry(PagemapEntry *entry, int pagemap_fd, uintptr_t vaddr)
+{
+	size_t nread;
+	ssize_t ret;
+	uint64_t data;
+
+	nread = 0;
+	while (nread < sizeof(data)) {
+		ret = pread(pagemap_fd, &data, sizeof(data),
+				(vaddr / sysconf(_SC_PAGE_SIZE)) * sizeof(data) + nread);
+		nread += ret;
+		if (ret <= 0) {
+			return 1;
+		}
+	}
+	entry->pfn = data & (((uint64_t)1 << 54) - 1);
+	entry->soft_dirty = (data >> 54) & 1;
+	entry->file_page = (data >> 61) & 1;
+	entry->swapped = (data >> 62) & 1;
+	entry->present = (data >> 63) & 1;
+	return 0;
+}
+
+/* Convert the given virtual address to physical using /proc/PID/pagemap.
+ *
+ * @param[out] paddr physical address
+ * @param[in]  pid   process to convert for
+ * @param[in] vaddr virtual address to get entry for
+ * @return 0 for success, 1 for failure
+ */
+int virt_to_phys_user(uintptr_t *paddr, pid_t pid, uintptr_t vaddr)
+{
+	char pagemap_file[BUFSIZ];
+	int pagemap_fd;
+
+	snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid);
+	pagemap_fd = open(pagemap_file, O_RDONLY);
+	if (pagemap_fd < 0) {
+		return 1;
+	}
+	PagemapEntry entry;
+	if (pagemap_get_entry(&entry, pagemap_fd, vaddr)) {
+		return 1;
+	}
+	close(pagemap_fd);
+	*paddr = (entry.pfn * sysconf(_SC_PAGE_SIZE)) + (vaddr % sysconf(_SC_PAGE_SIZE));
+	return 0;
+}
+
+#endif

kernel_module/user/mmap.c

@@ -2,10 +2,13 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h> /* uintmax_t */
 #include <string.h>
 #include <sys/mman.h>
 #include <unistd.h> /* sysconf */
 
+#include "common.h" /* virt_to_phys_user */
+
 enum { BUFFER_SIZE = 4 };
 
 int main(int argc, char **argv)
@@ -14,6 +17,7 @@ int main(int argc, char **argv)
 	long page_size;
 	char *address1, *address2;
 	char buf[BUFFER_SIZE];
+	uintptr_t paddr;
 
 	if (argc < 2) {
 		printf("Usage: %s <mmap_file>\n", argv[0]);
@@ -54,6 +58,13 @@ int main(int argc, char **argv)
 	/* Also modified. So both virtual addresses point to the same physical address. */
 	assert(!strcmp(address2, "qwer"));
 
+	/* Check that the physical addresses are the same.
+	 * They are, but TODO why virt_to_phys on kernel gives a different value? */
+	assert(!virt_to_phys_user(&paddr, getpid(), (uintptr_t)address1));
+	printf("paddr1 = 0x%jx\n", (uintmax_t)paddr);
+	assert(!virt_to_phys_user(&paddr, getpid(), (uintptr_t)address2));
+	printf("paddr2 = 0x%jx\n", (uintmax_t)paddr);
+
     /* Check that modifications made from userland are also visible from the kernel. */
 	read(fd, buf, BUFFER_SIZE);
 	assert(!memcmp(buf, "qwer", BUFFER_SIZE));

kernel_module/user/pagemap_dump.c

@@ -3,7 +3,8 @@ Only tested in x86_64.
 
 Adapted from: https://github.com/dwks/pagemap/blob/8a25747bc79d6080c8b94eac80807a4dceeda57a/pagemap2.c
 
-https://stackoverflow.com/questions/17021214/how-to-decode-proc-pid-pagemap-entries-in-linux/45126141#45126141
+- https://stackoverflow.com/questions/17021214/how-to-decode-proc-pid-pagemap-entries-in-linux/45126141#45126141
+- https://stackoverflow.com/questions/5748492/is-there-any-api-for-determining-the-physical-address-from-virtual-address-in-li
 
 Dump the page map of a given process PID.
 
@@ -13,106 +14,79 @@ Data sources: /proc/PIC/{map,pagemap}
 #define _POSIX_C_SOURCE 200809L
 #include <errno.h>
 #include <fcntl.h>
-#include <stdint>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/types.h>
 #include <unistd.h>
 
-typedef struct {
-    uint64_t phys : 54;
-    int soft_dirty : 1;
-    int padding : 4;
-    int padding : 1;
-
-    * Bit  61    page is file-page or shared-anon (since 3.5)
-    * Bit  62    page swapped
-    * Bit  63    page present
-} PagemapEntry;
-
-
-int parse_pagemap(PagemapEntry &entry, int fd, size_t offset)
-{
-    if (pread(pagemap, &data, ) != sizeof(data)) {
-        perror("pread");
-        break;
-    }
-
-    data & 0x7fffffffffffff,
-    (data >> 55) & 1,
-    (data >> 61) & 1,
-    (data >> 62) & 1,
-    (data >> 63) & 1,
-
-}
+#include "common.h" /* pagemap_get_entry */
 
 int main(int argc, char **argv) {
 	char buffer[BUFSIZ];
 	char maps_file[BUFSIZ];
 	char pagemap_file[BUFSIZ];
-	int maps;
+	int maps_fd;
 	int offset = 0;
-	int pagemap;
-	long page_size;
+	int pagemap_fd;
+	pid_t pid;
 
 	if (argc < 2) {
 		printf("Usage: %s pid\n", argv[0]);
 		return EXIT_FAILURE;
 	}
-	pid_t pid = (pid_t)strtoul(argv[1], NULL, 0);
-	snprintf(maps_file, sizeof(maps_file), "/proc/%lu/maps", (unsigned long)pid);
-	snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%lu/pagemap", (unsigned long)pid);
-	maps = open(maps_file, O_RDONLY);
-	if (maps < 0) {
+	pid = strtoull(argv[1], NULL, 0);
+	snprintf(maps_file, sizeof(maps_file), "/proc/%ju/maps", (uintmax_t)pid);
+	snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid);
+	maps_fd = open(maps_file, O_RDONLY);
+	if (maps_fd < 0) {
 		perror("open maps");
 		return EXIT_FAILURE;
 	}
-	pagemap = open(pagemap_file, O_RDONLY);
-	if (pagemap < 0) {
+	pagemap_fd = open(pagemap_file, O_RDONLY);
+	if (pagemap_fd < 0) {
 		perror("open pagemap");
 		return EXIT_FAILURE;
 	}
-	page_size = sysconf(_SC_PAGE_SIZE);
 	printf("addr pfn soft-dirty file/shared swapped present library\n");
 	for (;;) {
-		ssize_t length = read(maps, buffer + offset, sizeof buffer - offset);
+		ssize_t length = read(maps_fd, buffer + offset, sizeof buffer - offset);
 		if (length <= 0) break;
 		length += offset;
 		for (size_t i = offset; i < (size_t)length; i++) {
-			unsigned long low = 0, high = 0;
+			uintptr_t low = 0, high = 0;
 			if (buffer[i] == '\n' && i) {
 				const char *lib_name;
 				size_t y;
 				/* Parse a line from maps. Each line contains a range that contains many pages. */
 				{
 					size_t x = i - 1;
-					while(x && buffer[x] != '\n') x --;
+					while (x && buffer[x] != '\n') x--;
 					if (buffer[x] == '\n') x++;
 					size_t beginning = x;
-					while(buffer[x] != '-' && x < sizeof buffer) {
+					while (buffer[x] != '-' && x < sizeof buffer) {
 						char c = buffer[x++];
 						low *= 16;
 						if (c >= '0' && c <= '9') {
 							low += c - '0';
-						}
-						else if (c >= 'a' && c <= 'f') {
+						} else if (c >= 'a' && c <= 'f') {
 							low += c - 'a' + 10;
 						} else {
 						    break;
 						}
 					}
-					while(buffer[x] != '-' && x < sizeof buffer) x++;
+					while (buffer[x] != '-' && x < sizeof buffer) x++;
 					if (buffer[x] == '-') x++;
-					while(buffer[x] != ' ' && x < sizeof buffer) {
+					while (buffer[x] != ' ' && x < sizeof buffer) {
 						char c = buffer[x++];
 						high *= 16;
 						if (c >= '0' && c <= '9') {
 							high += c - '0';
-						}
-						else if (c >= 'a' && c <= 'f') {
+						} else if (c >= 'a' && c <= 'f') {
 							high += c - 'a' + 10;
+						} else {
+							break;
 						}
-						else break;
 					}
 					lib_name = 0;
 					for (int field = 0; field < 4; field++) {
@@ -127,27 +101,27 @@ int main(int argc, char **argv) {
 				}
 				/* Get info about all pages in this page range with pagemap. */
 				{
-					unsigned long data;
 					PagemapEntry entry;
-					for (unsigned long i = low; i < high; i += page_size) {
-						unsigned long index = (i / page_size) * sizeof(data);
-						parse_pagemap(&entry, pagemap, sizeof(data) * index);
-						printf("%lx %lx %d %d %d %d %s\n",
-							i,
-							data & 0x7fffffffffffff,
-							(data >> 55) & 1,
-							(data >> 61) & 1,
-							(data >> 62) & 1,
-							(data >> 63) & 1,
+					for (uintptr_t addr = low; addr < high; addr += sysconf(_SC_PAGE_SIZE)) {
+						/* TODO always fails for the last page (vsyscall), why? pread returns 0. */
+						if (!pagemap_get_entry(&entry, pagemap_fd, addr)) {
+							printf("%jx %jx %u %u %u %u %s\n",
+								(uintmax_t)addr,
+								(uintmax_t)entry.pfn,
+								entry.soft_dirty,
+								entry.file_page,
+								entry.swapped,
+								entry.present,
 								lib_name
 							);
 						}
 					}
+				}
 				buffer[y] = '\n';
 			}
 		}
 	}
-	close(maps);
-	close(pagemap);
-	return 0;
+	close(maps_fd);
+	close(pagemap_fd);
+	return EXIT_SUCCESS;
 }

kernel_module/user/virt_to_phys_user.c

@@ -0,0 +1,29 @@
+/*
+Convert a virtual address to physical for a given process PID using /proc/PID/pagemap.
+
+https://stackoverflow.com/questions/5748492/is-there-any-api-for-determining-the-physical-address-from-virtual-address-in-li/45128487#45128487
+*/
+
+#include <stdio.h> /* printf */
+#include <stdlib.h> /* EXIT_SUCCESS, EXIT_FAILURE, strtoull */
+
+#include "common.h" /* virt_to_phys_user */
+
+int main(int argc, char **argv)
+{
+	pid_t pid;
+	uintptr_t vaddr, paddr;
+
+	if (argc < 3) {
+		printf("Usage: %s pid vaddr\n", argv[0]);
+		return EXIT_FAILURE;
+	}
+	pid = strtoull(argv[1], NULL, 0);
+	vaddr = strtoull(argv[2], NULL, 0);
+	if (virt_to_phys_user(&paddr, pid, vaddr)) {
+		fprintf(stderr, "error: virt_to_phys_user\n");
+		return EXIT_FAILURE;
+	};
+	printf("0x%jx\n", (uintmax_t)paddr);
+	return EXIT_SUCCESS;
+}