From: "Borislav Petkov (AMD)" bp@alien8.de

commit d2408e043e7296017420aa5929b3bba4d5e61013 upstream.

Instead of decoding each instruction in the return sites range only to realize that that return site is a jump to the default return thunk which is needed - X86_FEATURE_RETHUNK is enabled - lift that check before the loop and get rid of that loop overhead.

Add comments about what gets patched, while at it.

Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lore.kernel.org/r/20230512120952.7924-1-bp@alien8.de Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com --- arch/x86/kernel/alternative.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 44bff34f7d10cb6868ad079ca1cb87e458d3f91b..dfd5490df0af9e55d1a6ab185ad7cb03bdda4a91 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -769,13 +769,12 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes) { int i = 0;

+ /* Patch the custom return thunks... */ if (cpu_wants_rethunk_at(addr)) { - if (x86_return_thunk == __x86_return_thunk) - return -1; - i = JMP32_INSN_SIZE; __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i); } else { + /* ... or patch them out if not needed. */ bytes[i++] = RET_INSN_OPCODE; }

@@ -788,6 +787,14 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end) { s32 *s;

+ /* + * Do not patch out the default return thunks if those needed are the + * ones generated by the compiler. + */ + if (cpu_feature_enabled(X86_FEATURE_RETHUNK) && + (x86_return_thunk == __x86_return_thunk)) + return; + for (s = start; s < end; s++) { void *dest = NULL, *addr = (void *)s + *s; struct insn insn;

From: Josh Poimboeuf jpoimboe@kernel.org

commit 4ba89dd6ddeca2a733bdaed7c9a5cbe4e19d9124 upstream.

The following commit

095b8303f383 ("x86/alternative: Make custom return thunk unconditional")

made '__x86_return_thunk' a placeholder value. All code setting X86_FEATURE_RETHUNK also changes the value of 'x86_return_thunk'. So the optimization at the beginning of apply_returns() is dead code.

Also, before the above-mentioned commit, the optimization actually had a bug It bypassed __static_call_fixup(), causing some raw returns to remain unpatched in static call trampolines. Thus the 'Fixes' tag.

Fixes: d2408e043e72 ("x86/alternative: Optimize returns patching") Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Acked-by: Borislav Petkov (AMD) bp@alien8.de Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.169388998... Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com --- arch/x86/kernel/alternative.c | 8 -------- 1 file changed, 8 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index dfd5490df0af9e55d1a6ab185ad7cb03bdda4a91..023899e9ebd16ba223a1de91da9bcb43666788f9 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -787,14 +787,6 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end) { s32 *s;

- /* - * Do not patch out the default return thunks if those needed are the - * ones generated by the compiler. - */ - if (cpu_feature_enabled(X86_FEATURE_RETHUNK) && - (x86_return_thunk == __x86_return_thunk)) - return; - for (s = start; s < end; s++) { void *dest = NULL, *addr = (void *)s + *s; struct insn insn;

From: Eric Biggers ebiggers@google.com

commit 9f35e33144ae5377d6a8de86dd3bd4d995c6ac65 upstream.

Fix several build errors when CONFIG_MODULES=n, including the following:

../arch/x86/kernel/alternative.c:195:25: error: incomplete definition of type 'struct module' 195 | for (int i = 0; i < mod->its_num_pages; i++) {

Fixes: 872df34d7c51 ("x86/its: Use dynamic thunks for indirect branches") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@google.com Acked-by: Dave Hansen dave.hansen@intel.com Tested-by: Steven Rostedt (Google) rostedt@goodmis.org Reviewed-by: Alexandre Chartre alexandre.chartre@oracle.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com --- arch/x86/kernel/alternative.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 023899e9ebd16ba223a1de91da9bcb43666788f9..843bda0cb5d09a091a06ac7c3b30d5545880e905 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -402,7 +402,9 @@ static int emit_indirect(int op, int reg, u8 *bytes)

#ifdef CONFIG_MITIGATION_ITS

+#ifdef CONFIG_MODULES static struct module *its_mod; +#endif static void *its_page; static unsigned int its_offset;

@@ -423,6 +425,7 @@ static void *its_init_thunk(void *thunk, int reg) return thunk; }

+#ifdef CONFIG_MODULES void its_init_mod(struct module *mod) { if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS)) @@ -462,6 +465,7 @@ void its_free_mod(struct module *mod) } kfree(mod->its_page_array); } +#endif /* CONFIG_MODULES */

DEFINE_FREE(its_execmem, void *, if (_T) module_memfree(_T));

@@ -472,6 +476,7 @@ static void *its_alloc(void) if (!page) return NULL;

+#ifdef CONFIG_MODULES if (its_mod) { void *tmp = krealloc(its_mod->its_page_array, (its_mod->its_num_pages+1) * sizeof(void *), @@ -482,6 +487,7 @@ static void *its_alloc(void) its_mod->its_page_array = tmp; its_mod->its_page_array[its_mod->its_num_pages++] = page; } +#endif /* CONFIG_MODULES */

return no_free_ptr(page); }