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x86/amd: Use IBPB for firmware calls

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commit 28a99e95f55c61855983d36a88c05c178d966bb7 upstream.

On AMD IBRS does not prevent Retbleed; as such use IBPB before a
firmware call to flush the branch history state.

And because in order to do an EFI call, the kernel maps a whole lot of
the kernel page table into the EFI page table, do an IBPB just in case
in order to prevent the scenario of poisoning the BTB and causing an EFI
call using the unprotected RET there.

  [ bp: Massage. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220715194550.793957-1-cascardo@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Zijlstra
2022-07-18 13:41:37 +02:00
committed by Greg Kroah-Hartman
parent 14fc9233aa
commit b7b9e5cc8b
3 changed files with 13 additions and 1 deletions
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11
arch/x86/kernel/cpu/bugs.c
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@@ -1475,7 +1475,16 @@ static void __init spectre_v2_select_mitigation(void)
* the CPU supports Enhanced IBRS, kernel might un-intentionally not
* enable IBRS around firmware calls.
*/
if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
if (boot_cpu_has_bug(X86_BUG_RETBLEED) &&
(boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)) {
if (retbleed_cmd != RETBLEED_CMD_IBPB) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB_FW);
pr_info("Enabling Speculation Barrier for firmware calls\n");
}
} else if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
pr_info("Enabling Restricted Speculation for firmware calls\n");
}