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| author | Peter Zijlstra <peterz@infradead.org> | 2024-10-14 20:05:48 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-18 09:24:59 +0300 |
| commit | 88a817e60dbbda17135800adf9704d0bdcbcf98f (patch) | |
| tree | 9c2b2282b4b57cd3f161b8f1882875cef73ee170 /include/linux/execmem.h | |
| parent | 15335117c5d73a0cc0404056c94cc8b6a371e25a (diff) | |
| download | linux-88a817e60dbbda17135800adf9704d0bdcbcf98f.tar.xz | |
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_ROX is not supported on backport kernel, made
adjustments to set memory to RW and ROX ]
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/execmem.h')
| -rw-r--r-- | include/linux/execmem.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/execmem.h b/include/linux/execmem.h index 32cef1144117..584e112ca380 100644 --- a/include/linux/execmem.h +++ b/include/linux/execmem.h @@ -4,6 +4,7 @@ #include <linux/types.h> #include <linux/moduleloader.h> +#include <linux/cleanup.h> #if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \ !defined(CONFIG_KASAN_VMALLOC) @@ -123,6 +124,8 @@ void *execmem_alloc(enum execmem_type type, size_t size); */ void execmem_free(void *ptr); +DEFINE_FREE(execmem, void *, if (_T) execmem_free(_T)); + #if defined(CONFIG_EXECMEM) && !defined(CONFIG_ARCH_WANTS_EXECMEM_LATE) void execmem_init(void); #else |