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Kernel: Always inline stac(), clac() and SmapDisabler

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Let's not be paying the function call overhead for these tiny ops.
Maybe there's an argument for having fewer gadgets in the kernel but
for now we're actually seeing stac() in profiles so let's put
that above theoretical security issues.
This commit is contained in:
Andreas Kling 2020-05-20 14:14:02 +02:00
parent e10183a6c5
commit 81d35c6891
Notes: sideshowbarker 2024-07-19 06:19:25 +09:00
2 changed files with 17 additions and 20 deletions
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16
Kernel/Arch/i386/CPU.cpp
View file

@ -734,22 +734,6 @@ void cpu_detect()
g_cpu_supports_umip = (extended_features.ecx() & (1 << 2));
}
void stac()
{
if (!g_cpu_supports_smap)
return;
asm volatile("stac" ::
: "cc");
}
void clac()
{
if (!g_cpu_supports_smap)
return;
asm volatile("clac" ::
: "cc");
}
void cpu_setup()
{
cpu_detect();

21
Kernel/Arch/i386/CPU.h
View file

@ -584,18 +584,31 @@ extern bool g_cpu_supports_sse;
extern bool g_cpu_supports_tsc;
extern bool g_cpu_supports_umip;
void stac();
void clac();
ALWAYS_INLINE void stac()
{
if (!g_cpu_supports_smap)
return;
asm volatile("stac" ::
: "cc");
}
ALWAYS_INLINE void clac()
{
if (!g_cpu_supports_smap)
return;
asm volatile("clac" ::
: "cc");
}
class SmapDisabler {
public:
SmapDisabler()
ALWAYS_INLINE SmapDisabler()
{
m_flags = cpu_flags();
stac();
}
~SmapDisabler()
ALWAYS_INLINE ~SmapDisabler()
{
if (!(m_flags & 0x40000))
clac();