diff options
| author | Pawan Gupta <pawan.kumar.gupta@linux.intel.com> | 2025-05-03 09:46:31 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-18 08:21:26 +0200 |
| commit | 9502e83c22bef5ecfb2386aaa837d8afcf1fcece (patch) | |
| tree | f5bc6d421de56c36ddf758f761e68deac97cec0e | |
| parent | e6da4a83e3689e963f115c0a8cff5da6f5b51256 (diff) | |
x86/ibt: Keep IBT disabled during alternative patching
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>
| -rw-r--r-- | arch/x86/kernel/alternative.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index d70129eea923..f46db81b55b0 100644 --- 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_selftest(void) void __init alternative_instructions(void) { + u64 ibt; + int3_selftest(); /* @@ -1043,6 +1046,9 @@ void __init alternative_instructions(void) */ 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(void) 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)) { |