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Commit 7eb3e2a8 authored by Pawan Gupta's avatar Pawan Gupta Committed by Greg Kroah-Hartman
Browse files

x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts 



commit eb23b5ef9131e6d65011de349a4d25ef1b3d4314 upstream.

IBRS mitigation for spectre_v2 forces write to MSR_IA32_SPEC_CTRL at
every kernel entry/exit. On Enhanced IBRS parts setting
MSR_IA32_SPEC_CTRL[IBRS] only once at boot is sufficient. MSR writes at
every kernel entry/exit incur unnecessary performance loss.

When Enhanced IBRS feature is present, print a warning about this
unnecessary performance loss.

Signed-off-by: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThadeu Lima de Souza Cascardo <cascardo@canonical.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/2a5eaf54583c2bfe0edc4fea64006656256cca17.1657814857.git.pawan.kumar.gupta@linux.intel.com


Signed-off-by: default avatarThadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: default avatarSuleiman Souhlal <suleiman@google.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0019a40f

arch/x86/kernel/cpu/bugs.c

+3 −0
Original line number Diff line number Diff line
@@ -851,6 +851,7 @@ static inline const char *spectre_v2_module_string(void) { return ""; } 
#define SPECTRE_V2_LFENCE_MSG "WARNING: LFENCE mitigation is not recommended for this CPU, data leaks possible!\n"

#define SPECTRE_V2_EIBRS_EBPF_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS on, data leaks possible via Spectre v2 BHB attacks!\n"

#define SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS+LFENCE mitigation and SMT, data leaks possible via Spectre v2 BHB attacks!\n"

#define SPECTRE_V2_IBRS_PERF_MSG "WARNING: IBRS mitigation selected on Enhanced IBRS CPU, this may cause unnecessary performance loss\n"



#ifdef CONFIG_BPF_SYSCALL

void unpriv_ebpf_notify(int new_state)
@@ -1277,6 +1278,8 @@ static void __init spectre_v2_select_mitigation(void) 


	case SPECTRE_V2_IBRS:

		setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS);

		if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED))

			pr_warn(SPECTRE_V2_IBRS_PERF_MSG);

		break;



	case SPECTRE_V2_LFENCE: