6.1-stable review patch. If anyone has any objections, please let me know.
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From: Pawan Gupta pawan.kumar.gupta@linux.intel.com
commit ebebe30794d38c51f71fe4951ba6af4159d9837d upstream.
cfi_rewrite_callers() updates the fineIBT hash matching at the caller side, but except for paranoid-mode it relies on apply_retpoline() and friends for any ENDBR relocation. This could temporarily cause an indirect branch to land on a poisoned ENDBR.
For instance, with para-virtualization enabled, a simple wrmsrl() could have an indirect branch pointing to native_write_msr() who's ENDBR has been relocated due to fineIBT:
<wrmsrl>: push %rbp mov %rsp,%rbp mov %esi,%eax mov %rsi,%rdx shr $0x20,%rdx mov %edi,%edi mov %rax,%rsi call *0x21e65d0(%rip) # <pv_ops+0xb8> ^^^^^^^^^^^^^^^^^^^^^^^
Such an indirect call during the alternative patching could #CP if the caller is not *yet* adjusted for the new target ENDBR. To prevent a false #CP, keep CET-IBT disabled until all callers are patched.
Patching during the module load does not need to be guarded by IBT-disable because the module code is not executed until the patching is complete.
[ pawan: Since apply_paravirt() happens before __apply_fineibt() relocates the ENDBR, pv_ops in the example above is not relevant. It is still safer to keep this commit because missing an ENDBR means an oops. ]
Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Alexandre Chartre alexandre.chartre@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/alternative.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -30,6 +30,7 @@ #include <asm/fixmap.h> #include <asm/paravirt.h> #include <asm/asm-prototypes.h> +#include <asm/cfi.h>
int __read_mostly alternatives_patched;
@@ -1006,6 +1007,8 @@ static noinline void __init int3_selftes
void __init alternative_instructions(void) { + u64 ibt; + int3_selftest();
/* @@ -1043,6 +1046,9 @@ void __init alternative_instructions(voi */ paravirt_set_cap();
+ /* Keep CET-IBT disabled until caller/callee are patched */ + ibt = ibt_save(); + /* * First patch paravirt functions, such that we overwrite the indirect * call with the direct call. @@ -1064,6 +1070,8 @@ void __init alternative_instructions(voi
apply_ibt_endbr(__ibt_endbr_seal, __ibt_endbr_seal_end);
+ ibt_restore(ibt); + #ifdef CONFIG_SMP /* Patch to UP if other cpus not imminent. */ if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) {