diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2024-10-14 10:05:48 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-18 08:24:11 +0200 |
| commit | 3b2234cd50a9b4ed664324054901b6f763890104 (patch) | |
| tree | 56da30cd0f98d209bd7471ac6758c60e28658a56 /include/linux | |
| parent | 6699bf27a47156baafde7e3f4a732aab2ad9f8cb (diff) | |
x86/its: Use dynamic thunks for indirect branches
commit 872df34d7c51a79523820ea6a14860398c639b87 upstream.
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.
[ pawan: CONFIG_EXECMEM and CONFIG_EXECMEM_ROX are not supported on
backport kernel, made changes to use module_alloc() and
set_memory_*() for dynamic thunks. ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/module.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/module.h b/include/linux/module.h index f2a8624eef1e..f58d1eb260fa 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -572,6 +572,11 @@ struct module { atomic_t refcnt; #endif +#ifdef CONFIG_MITIGATION_ITS + int its_num_pages; + void **its_page_array; +#endif + #ifdef CONFIG_CONSTRUCTORS /* Constructor functions. */ ctor_fn_t *ctors; |