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- Enable the short string copies for CPUs which support them, in

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copy_user_enhanced_fast_string()
 
 - Avoid writing MSR_CSTAR on Intel due to TDX guests raising a #VE trap
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Merge tag 'x86_cpu_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 cpuid updates from Borislav Petkov:

 - Enable the short string copies for CPUs which support them, in
   copy_user_enhanced_fast_string()

 - Avoid writing MSR_CSTAR on Intel due to TDX guests raising a #VE trap

* tag 'x86_cpu_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/lib: Add fast-short-rep-movs check to copy_user_enhanced_fast_string()
  x86/cpu: Don't write CSTAR MSR on Intel CPUs
This commit is contained in:
Linus Torvalds 2022-01-10 10:09:22 -08:00
commit 25f8c7785e
2 changed files with 15 additions and 4 deletions
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15
arch/x86/kernel/cpu/common.c
View File

@ -1787,6 +1787,17 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count);
DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) = TOP_OF_INIT_STACK;
static void wrmsrl_cstar(unsigned long val)
{
/*
* Intel CPUs do not support 32-bit SYSCALL. Writing to MSR_CSTAR
* is so far ignored by the CPU, but raises a #VE trap in a TDX
* guest. Avoid the pointless write on all Intel CPUs.
*/
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
wrmsrl(MSR_CSTAR, val);
}
/* May not be marked __init: used by software suspend */
void syscall_init(void)
{
@ -1794,7 +1805,7 @@ void syscall_init(void)
wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);
#ifdef CONFIG_IA32_EMULATION
wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);
wrmsrl_cstar((unsigned long)entry_SYSCALL_compat);
/*
* This only works on Intel CPUs.
* On AMD CPUs these MSRs are 32-bit, CPU truncates MSR_IA32_SYSENTER_EIP.
@ -1806,7 +1817,7 @@ void syscall_init(void)
(unsigned long)(cpu_entry_stack(smp_processor_id()) + 1));
wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
#else
wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
wrmsrl_cstar((unsigned long)ignore_sysret);
wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);

4
arch/x86/lib/copy_user_64.S
View File

@ -200,8 +200,8 @@ EXPORT_SYMBOL(copy_user_generic_string)
*/
SYM_FUNC_START(copy_user_enhanced_fast_string)
ASM_STAC
cmpl $64,%edx
jb .L_copy_short_string /* less then 64 bytes, avoid the costly 'rep' */
/* CPUs without FSRM should avoid rep movsb for short copies */
ALTERNATIVE "cmpl $64, %edx; jb .L_copy_short_string", "", X86_FEATURE_FSRM
movl %edx,%ecx
1: rep
movsb