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Subject[PATCH] x86/microcode: Refactor Intel microcode loading
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This changes generic_load_microcode() to use the iov_iter API instead of
an open-coded version. This allows us to avoid explicitly casting between
user and kernel pointers.

Because the iov_iter API makes it hard to read the same location twice, as
a side effect, this also fixes 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 can do this anyway...

Signed-off-by: Jann Horn <jannh@google.com>
---
I have tested that with this patch applied, microcode loading still works
both via "iucode-tool -k" and via
/sys/devices/system/cpu/microcode/reload.

arch/x86/kernel/cpu/microcode/intel.c | 64 +++++++++++++--------------
1 file changed, 32 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 16936a24795c..cb976e8ef94d 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 @@ static enum ucode_state apply_microcode_intel(int cpu)
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;
+ u8 *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;

- 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\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);
@@ -981,6 +976,8 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
struct cpuinfo_x86 *c = &cpu_data(cpu);
const struct firmware *firmware;
enum ucode_state ret;
+ struct kvec kvec;
+ struct iov_iter iter;

if (is_blacklisted(cpu))
return UCODE_NFOUND;
@@ -993,26 +990,29 @@ 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 iovec iov;
+ struct iov_iter iter;
+
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 = {
--
2.21.0.392.gf8f6787159e-goog
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