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x86/mitigations: Clear CPU buffers on the SYSCALL fast path

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The fast SYSCALL exit path returns with SYSRET to userspace after
verifying that there's no pending work. MDS mitigation mandates that CPU
buffers must be cleared on transition from kernel to userspace so do
that here too.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Borislav Petkov 2020-04-19 09:59:03 +02:00 committed by Greg Kroah-Hartman
parent 5706d13e27
commit 58fb3c3589
3 changed files with 9 additions and 0 deletions
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2
arch/x86/entry/entry_64.S
View File

@ -218,6 +218,8 @@ entry_SYSCALL_64_fastpath:
testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
jnz int_ret_from_sys_call_irqs_off /* Go to the slow path */
call mds_user_clear_buffers
movq RIP(%rsp), %rcx
movq EFLAGS(%rsp), %r11
RESTORE_C_REGS_EXCEPT_RCX_R11

2
arch/x86/include/asm/spec-ctrl.h
View File

@ -85,4 +85,6 @@ static inline void speculative_store_bypass_ht_init(void) { }
extern void speculation_ctrl_update(unsigned long tif);
extern void speculation_ctrl_update_current(void);
extern void mds_user_clear_buffers(void);
#endif

5
arch/x86/kernel/cpu/bugs.c
View File

@ -263,6 +263,11 @@ static int __init mds_cmdline(char *str)
}
early_param("mds", mds_cmdline);
void mds_user_clear_buffers(void)
{
mds_user_clear_cpu_buffers();
}
#undef pr_fmt
#define pr_fmt(fmt) "TAA: " fmt