x86/microcode/intel: Refactor Intel microcode blob loading

Change generic_load_microcode() to use the iov_iter API instead of a
clumsy open-coded version which has to pay attention to __user data
or kernel data, depending on the loading method. This allows to avoid
explicit casting between user and kernel pointers.

Because the iov_iter API makes it hard to read the same location twice,
as a side effect, also fix a double-read of the microcode header (which
could e.g. lead to out-of-bounds reads in microcode_sanity_check()).

Not that it matters much, only root is allowed to load microcode
anyway...

 [ bp: Massage a bit, sort function-local variables. ]

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190404111128.131157-1-jannh@google.com

1 files changed, 36 insertions, 35 deletions

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 16936a24795c..a44bdbe7c55e 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -31,6 +31,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/cpu.h>
+#include <linux/uio.h>
 #include <linux/mm.h>
 
 #include <asm/microcode_intel.h>
@@ -861,32 +862,33 @@ out:
         return ret;
 }
 
-static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
-                                int (*get_ucode_data)(void *, const void *, size_t))
+static enum ucode_state generic_load_microcode(int cpu, struct iov_iter *iter)
 {
         struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
-        u8 *ucode_ptr = data, *new_mc = NULL, *mc = NULL;
-        int new_rev = uci->cpu_sig.rev;
-        unsigned int leftover = size;
         unsigned int curr_mc_size = 0, new_mc_size = 0;
-        unsigned int csig, cpf;
         enum ucode_state ret = UCODE_OK;
+        int new_rev = uci->cpu_sig.rev;
+        u8 *new_mc = NULL, *mc = NULL;
+        unsigned int csig, cpf;
 
-        while (leftover) {
+        while (iov_iter_count(iter)) {
                 struct microcode_header_intel mc_header;
-                unsigned int mc_size;
+                unsigned int mc_size, data_size;
+                u8 *data;
 
-                if (leftover < sizeof(mc_header)) {
-                        pr_err("error! Truncated header in microcode data file\n");
+                if (!copy_from_iter_full(&mc_header, sizeof(mc_header), iter)) {
+                        pr_err("error! Truncated or inaccessible header in microcode data file\n");
                         break;
                 }
 
-                if (get_ucode_data(&mc_header, ucode_ptr, sizeof(mc_header)))
-                        break;
-
                 mc_size = get_totalsize(&mc_header);
-                if (!mc_size || mc_size > leftover) {
-                        pr_err("error! Bad data in microcode data file\n");
+                if (mc_size < sizeof(mc_header)) {
+                        pr_err("error! Bad data in microcode data file (totalsize too small)\n");
+                        break;
+                }
+                data_size = mc_size - sizeof(mc_header);
+                if (data_size > iov_iter_count(iter)) {
+                        pr_err("error! Bad data in microcode data file (truncated file?)\n");
                         break;
                 }
 
@@ -899,7 +901,9 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
                         curr_mc_size = mc_size;
                 }
 
-                if (get_ucode_data(mc, ucode_ptr, mc_size) ||
+                memcpy(mc, &mc_header, sizeof(mc_header));
+                data = mc + sizeof(mc_header);
+                if (!copy_from_iter_full(data, data_size, iter) ||
                     microcode_sanity_check(mc, 1) < 0) {
                         break;
                 }
@@ -914,14 +918,11 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
                         mc = NULL;      /* trigger new vmalloc */
                         ret = UCODE_NEW;
                 }
-
-                ucode_ptr += mc_size;
-                leftover  -= mc_size;
         }
 
         vfree(mc);
 
-        if (leftover) {
+        if (iov_iter_count(iter)) {
                 vfree(new_mc);
                 return UCODE_ERROR;
         }
@@ -945,12 +946,6 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
         return ret;
 }
 
-static int get_ucode_fw(void *to, const void *from, size_t n)
-{
-        memcpy(to, from, n);
-        return 0;
-}
-
 static bool is_blacklisted(unsigned int cpu)
 {
         struct cpuinfo_x86 *c = &cpu_data(cpu);
@@ -977,10 +972,12 @@ static bool is_blacklisted(unsigned int cpu)
 static enum ucode_state request_microcode_fw(int cpu, struct device *device,
                                              bool refresh_fw)
 {
-        char name[30];
         struct cpuinfo_x86 *c = &cpu_data(cpu);
         const struct firmware *firmware;
+        struct iov_iter iter;
         enum ucode_state ret;
+        struct kvec kvec;
+        char name[30];
 
         if (is_blacklisted(cpu))
                 return UCODE_NFOUND;
@@ -993,26 +990,30 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
                 return UCODE_NFOUND;
         }
 
-        ret = generic_load_microcode(cpu, (void *)firmware->data,
-                                     firmware->size, &get_ucode_fw);
+        kvec.iov_base = (void *)firmware->data;
+        kvec.iov_len = firmware->size;
+        iov_iter_kvec(&iter, WRITE, &kvec, 1, firmware->size);
+        ret = generic_load_microcode(cpu, &iter);
 
         release_firmware(firmware);
 
         return ret;
 }
 
-static int get_ucode_user(void *to, const void *from, size_t n)
-{
-        return copy_from_user(to, from, n);
-}
-
 static enum ucode_state
 request_microcode_user(int cpu, const void __user *buf, size_t size)
 {
+        struct iov_iter iter;
+        struct iovec iov;
+
         if (is_blacklisted(cpu))
                 return UCODE_NFOUND;
 
-        return generic_load_microcode(cpu, (void *)buf, size, &get_ucode_user);
+        iov.iov_base = (void __user *)buf;
+        iov.iov_len = size;
+        iov_iter_init(&iter, WRITE, &iov, 1, size);
+
+        return generic_load_microcode(cpu, &iter);
 }
 
 static struct microcode_ops microcode_intel_ops = {