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Kernel: Disable x86 RDTSC instruction in userspace

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It's still possible to read the TSC via the read_tsc() syscall, but we
will now clear some of the bottom bits for unprivileged users.
This commit is contained in:
Andreas Kling 2020-01-01 18:18:02 +01:00
parent dfd759f75a
commit 38f93ef13b
6 changed files with 25 additions and 1 deletions
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2
Kernel/Arch/i386/CPU.cpp
View file

@ -526,6 +526,7 @@ bool g_cpu_supports_pae;
bool g_cpu_supports_pge;
bool g_cpu_supports_smep;
bool g_cpu_supports_sse;
bool g_cpu_supports_tsc;
bool g_cpu_supports_umip;
void detect_cpu_features()
@ -534,6 +535,7 @@ void detect_cpu_features()
g_cpu_supports_pae = (processor_info.edx() & (1 << 6));
g_cpu_supports_pge = (processor_info.edx() & (1 << 13));
g_cpu_supports_sse = (processor_info.edx() & (1 << 25));
g_cpu_supports_tsc = (processor_info.edx() & (1 << 4));
CPUID extended_processor_info(0x80000001);
g_cpu_supports_nx = (extended_processor_info.edx() & (1 << 20));

1
Kernel/Arch/i386/CPU.h
View file

@ -513,4 +513,5 @@ extern bool g_cpu_supports_pae;
extern bool g_cpu_supports_pge;
extern bool g_cpu_supports_smep;
extern bool g_cpu_supports_sse;
extern bool g_cpu_supports_tsc;
extern bool g_cpu_supports_umip;

2
Kernel/Process.cpp
View file

@ -2452,6 +2452,8 @@ int Process::sys$read_tsc(u32* lsw, u32* msw)
if (!validate_write_typed(msw))
return -EFAULT;
read_tsc(*lsw, *msw);
if (!is_superuser())
*lsw &= ~0xfff;
return 0;
}

8
Kernel/init.cpp
View file

@ -266,6 +266,14 @@ extern "C" [[noreturn]] void init(u32 physical_address_for_kernel_page_tables)
kprintf("x86: UMIP support enabled\n");
}
if (g_cpu_supports_tsc) {
asm volatile(
"mov %cr4, %eax\n"
"orl $0x4, %eax\n"
"mov %eax, %cr4\n");
kprintf("x86: RDTSC support restricted\n");
}
RTC::initialize();
PIC::initialize();
gdt_init();