diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2024-10-14 10:05:48 -0700 |
|---|---|---|
| committer | Dave Hansen <dave.hansen@linux.intel.com> | 2025-05-09 13:36:58 -0700 |
| commit | 872df34d7c51a79523820ea6a14860398c639b87 (patch) | |
| tree | 879a171d40e26b5c2258dea65914eb18b00aeb55 /arch/x86/kernel/module.c | |
| parent | ebebe30794d38c51f71fe4951ba6af4159d9837d (diff) | |
x86/its: Use dynamic thunks for indirect branches
ITS mitigation moves the unsafe indirect branches to a safe thunk. This
could degrade the prediction accuracy as the source address of indirect
branches becomes same for different execution paths.
To improve the predictions, and hence the performance, assign a separate
thunk for each indirect callsite. This is also a defense-in-depth measure
to avoid indirect branches aliasing with each other.
As an example, 5000 dynamic thunks would utilize around 16 bits of the
address space, thereby gaining entropy. For a BTB that uses
32 bits for indexing, dynamic thunks could provide better prediction
accuracy over fixed thunks.
Have ITS thunks be variable sized and use EXECMEM_MODULE_TEXT such that
they are both more flexible (got to extend them later) and live in 2M TLBs,
just like kernel code, avoiding undue TLB pressure.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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>
Diffstat (limited to 'arch/x86/kernel/module.c')
| -rw-r--r-- | arch/x86/kernel/module.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index a7998f351701..ff07558b7ebc 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -266,6 +266,8 @@ int module_finalize(const Elf_Ehdr *hdr, ibt_endbr = s; } + its_init_mod(me); + if (retpolines || cfi) { void *rseg = NULL, *cseg = NULL; unsigned int rsize = 0, csize = 0; @@ -286,6 +288,9 @@ int module_finalize(const Elf_Ehdr *hdr, void *rseg = (void *)retpolines->sh_addr; apply_retpolines(rseg, rseg + retpolines->sh_size); } + + its_fini_mod(me); + if (returns) { void *rseg = (void *)returns->sh_addr; apply_returns(rseg, rseg + returns->sh_size); @@ -326,4 +331,5 @@ int module_finalize(const Elf_Ehdr *hdr, void module_arch_cleanup(struct module *mod) { alternatives_smp_module_del(mod); + its_free_mod(mod); } |