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DateSat, 25 Dec 2010 19:57:41 +0100 (CET)
FromJesper Juhl <>
Subject[PATCH] Intel CPU Microcode Update Driver: Fix double vfree() and remove redundant pointer checks before vfree()
Hi,

In arch/x86/kernel/microcode_intel.c::generic_load_microcode() we have
this:

while (leftover) {
...
if (get_ucode_data(mc, ucode_ptr, mc_size) ||
microcode_sanity_check(mc) < 0) {
vfree(mc);
break;
}
...
}
if (mc)
vfree(mc);
This will cause a double free of 'mc'. This patch fixes that by just
removing the vfree() call in the loop since 'mc' will be freed nicely just
after we break out of the loop.

There's also a second change in the patch. I noticed a lot of checks for
pointers being NULL before passing them to vfree(). That's completely
redundant since vfree() deals gracefully with being passed a NULL pointer.
Removing the redundant checks yields a nice size decrease for the object
file.

Size before the patch:
text data bss dec hex filename
4578 240 1032 5850 16da arch/x86/kernel/microcode_intel.o
Size after the patch:
text data bss dec hex filename
4489 240 984 5713 1651 arch/x86/kernel/microcode_intel.o


Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
microcode_intel.c | 16 +++++-----------
1 file changed, 5 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kernel/microcode_intel.c b/arch/x86/kernel/microcode_intel.c
index dcb65cc..1a1b606 100644
--- a/arch/x86/kernel/microcode_intel.c
+++ b/arch/x86/kernel/microcode_intel.c
@@ -364,8 +364,7 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,

/* For performance reasons, reuse mc area when possible */
if (!mc || mc_size > curr_mc_size) {
- if (mc)
- vfree(mc);
+ vfree(mc);
mc = vmalloc(mc_size);
if (!mc)
break;
@@ -374,13 +373,11 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,

if (get_ucode_data(mc, ucode_ptr, mc_size) ||
microcode_sanity_check(mc) < 0) {
- vfree(mc);
break;
}

if (get_matching_microcode(&uci->cpu_sig, mc, new_rev)) {
- if (new_mc)
- vfree(new_mc);
+ vfree(new_mc);
new_rev = mc_header.rev;
new_mc = mc;
mc = NULL; /* trigger new vmalloc */
@@ -390,12 +387,10 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
leftover -= mc_size;
}

- if (mc)
- vfree(mc);
+ vfree(mc);

if (leftover) {
- if (new_mc)
- vfree(new_mc);
+ vfree(new_mc);
state = UCODE_ERROR;
goto out;
}
@@ -405,8 +400,7 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
goto out;
}

- if (uci->mc)
- vfree(uci->mc);
+ vfree(uci->mc);
uci->mc = (struct microcode_intel *)new_mc;

pr_debug("CPU%d found a matching microcode update with version 0x%x (current=0x%x)\n",


--
Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.



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