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kernel/x86_64: Always lfence after swapgs.

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This works around "yet another" Intel CPU bug. AMD is unaffected.
Linux chose to use an altcodepatch for Intel only; FreeBSD did
a bunch of benchmarks and determined the effect this had (if any)
was so far out in the decimal places that just adding it unconditionally
was the easier and simplest solution.

(FreeBSD commit: https://github.com/freebsd/freebsd/commit/f4038696064b86260)

Fixes #15236.
This commit is contained in:
Augustin Cavalier
2019-08-14 17:54:40 -04:00
parent 8c6b1519a2
commit 84f6e2d39f
2 changed files with 10 additions and 0 deletions
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src/system/kernel/arch/x86/64/entry_compat.S
+2
View File
@@ -152,6 +152,7 @@ FUNCTION_END(x86_64_syscall32_entry)
// ecx - user esp // ecx - user esp
FUNCTION(x86_64_sysenter32_entry): FUNCTION(x86_64_sysenter32_entry):
swapgs swapgs
lfence
// Set up an iframe on the stack (ECX = saved ESP). // Set up an iframe on the stack (ECX = saved ESP).
push $USER_DATA_SELECTOR // ss push $USER_DATA_SELECTOR // ss
@@ -314,6 +315,7 @@ FUNCTION(x86_64_sysenter32_entry):
// Restore previous GS base and return. // Restore previous GS base and return.
swapgs swapgs
lfence
sti sti
sysexit sysexit
src/system/kernel/arch/x86/64/interrupts.S
+8
View File
@@ -244,6 +244,7 @@ FUNCTION_END(int_bottom)
STATIC_FUNCTION(int_bottom_user): STATIC_FUNCTION(int_bottom_user):
// Load the kernel GS segment base. // Load the kernel GS segment base.
swapgs swapgs
lfence
// Push the rest of the interrupt frame to the stack. // Push the rest of the interrupt frame to the stack.
PUSH_IFRAME_BOTTOM(IFRAME_TYPE_OTHER) PUSH_IFRAME_BOTTOM(IFRAME_TYPE_OTHER)
@@ -293,6 +294,7 @@ STATIC_FUNCTION(int_bottom_user):
// Restore the previous GS base and return. // Restore the previous GS base and return.
swapgs swapgs
lfence
iretq iretq
.Lkernel_exit_work: .Lkernel_exit_work:
@@ -321,6 +323,7 @@ STATIC_FUNCTION(int_bottom_user):
// Restore the previous GS base and return. // Restore the previous GS base and return.
swapgs swapgs
lfence
iretq iretq
.Lkernel_exit_handle_signals: .Lkernel_exit_handle_signals:
@@ -340,6 +343,7 @@ FUNCTION(x86_64_syscall_entry):
// scratch space to store the user stack pointer in before we can push it // scratch space to store the user stack pointer in before we can push it
// to the stack. // to the stack.
swapgs swapgs
lfence
movq %rsp, %gs:ARCH_THREAD_user_rsp movq %rsp, %gs:ARCH_THREAD_user_rsp
movq %gs:ARCH_THREAD_syscall_rsp, %rsp movq %gs:ARCH_THREAD_syscall_rsp, %rsp
@@ -452,6 +456,7 @@ FUNCTION(x86_64_syscall_entry):
// Restore previous GS base and return. // Restore previous GS base and return.
swapgs swapgs
lfence
sysretq sysretq
.Lpre_syscall_debug: .Lpre_syscall_debug:
@@ -525,6 +530,7 @@ FUNCTION(x86_64_syscall_entry):
// Restore the previous GS base and return. // Restore the previous GS base and return.
swapgs swapgs
lfence
iretq iretq
.Lpost_syscall_handle_signals: .Lpost_syscall_handle_signals:
@@ -601,6 +607,7 @@ FUNCTION(x86_return_to_userland):
// Restore the frame and return. // Restore the frame and return.
RESTORE_IFRAME() RESTORE_IFRAME()
swapgs swapgs
lfence
iretq iretq
.Luserland_return_work: .Luserland_return_work:
// Slow path for return to userland. // Slow path for return to userland.
@@ -625,6 +632,7 @@ FUNCTION(x86_return_to_userland):
// Restore the previous GS base and return. // Restore the previous GS base and return.
swapgs swapgs
lfence
iretq iretq
.Luserland_return_handle_signals: .Luserland_return_handle_signals:
// thread_at_kernel_exit requires interrupts to be enabled, it will disable // thread_at_kernel_exit requires interrupts to be enabled, it will disable