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authorLinus Torvalds <torvalds@linux-foundation.org>2022-01-10 10:09:22 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2022-01-10 10:09:22 -0800
commit25f8c7785e254779fbd2127c4eced81811e8e421 (patch)
tree3b377bd739e5a7d94a2bb50398387a2322028d51
parent308319e990ae95b2a752fa0a1730f88598ca0dc7 (diff)
parent244122b4d2e5221e6abd6e21d6a58170104db781 (diff)
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
-rw-r--r--arch/x86/kernel/cpu/common.c15
-rw-r--r--arch/x86/lib/copy_user_64.S4
2 files changed, 15 insertions, 4 deletions
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 79b3d67addcc..7b8382c11788 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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);
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 2797e630b9b1..1c429f0489dd 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -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