When we collect a signal context with one of the SME modes enabled we will have enabled that mode behind the compiler and libc's back so they may issue some instructions not valid in streaming mode, causing spurious failures.

For the code prior to issuing the BRK to trigger signal handling we need to stay in streaming mode if we were already there since that's a part of the signal context the caller is trying to collect. Unfortunately this code includes a memset() which is likely to be heavily optimised and is likely to use FP instructions incompatible with streaming mode. We can avoid this happening by open coding the memset(), inserting a volatile assembly statement to avoid the compiler recognising what's being done and doing something in optimisation. This code is not performance critical so the inefficiency should not be an issue.

After collecting the context we can simply exit streaming mode, avoiding these issues. Use a full SMSTOP for safety to prevent any issues appearing with ZA.

Reported-by: Will Deacon will@kernel.org Signed-off-by: Mark Brown broonie@kernel.org --- .../selftests/arm64/signal/test_signals_utils.h | 25 +++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h index 222093f51b67..c7f5627171dd 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -60,13 +60,25 @@ static __always_inline bool get_current_context(struct tdescr *td, size_t dest_sz) { static volatile bool seen_already; + int i; + char *uc = (char *)dest_uc;

assert(td && dest_uc); /* it's a genuine invocation..reinit */ seen_already = 0; td->live_uc_valid = 0; td->live_sz = dest_sz; - memset(dest_uc, 0x00, td->live_sz); + + /* + * This is a memset() but we don't want the compiler to + * optimise it into either instructions or a library call + * which might be incompatible with streaming mode. + */ + for (i = 0; i < td->live_sz; i++) { + uc[i] = 0; + __asm__ ("" : "=r" (uc[i]) : "0" (uc[i])); + } + td->live_uc = dest_uc; /* * Grab ucontext_t triggering a SIGTRAP. @@ -103,6 +115,17 @@ static __always_inline bool get_current_context(struct tdescr *td, : : "memory");

+ /* + * If we were grabbing a streaming mode context then we may + * have entered streaming mode behind the system's back and + * libc or compiler generated code might decide to do + * something invalid in streaming mode, or potentially even + * the state of ZA. Issue a SMSTOP to exit both now we have + * grabbed the state. + */ + if (td->feats_supported & FEAT_SME) + asm volatile("msr S0_3_C4_C6_3, xzr"); + /* * If we get here with seen_already==1 it implies the td->live_uc * context has been used to get back here....this probably means

We don't have definitions of __always_unused or __noreturn in the tools version of compiler.h, add them so we can use them in kselftests.

Signed-off-by: Mark Brown broonie@kernel.org --- tools/include/linux/compiler.h | 12 ++++++++++++ 1 file changed, 12 insertions(+)

diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h index f75cced41d59..1684216e826a 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -42,6 +42,18 @@ # define __always_inline inline __attribute__((always_inline)) #endif

+#ifndef __always_unused +#define __always_unused __attribute__((__unused__)) +#endif + +#ifndef __noreturn +#define __noreturn __attribute__((__noreturn__)) +#endif + +#ifndef unreachable +#define unreachable() __builtin_unreachable() +#endif + #ifndef noinline #define noinline #endif

We had open coded the definition of OPTIMIZER_HIDE_VAR() as a fix but now that we have the generic tools/include available and that has had a definition of OPTIMIZER_HIDE_VAR() we can switch to the define.

Signed-off-by: Mark Brown broonie@kernel.org --- tools/testing/selftests/arm64/signal/test_signals_utils.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h index c7f5627171dd..762c8fe9c54a 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -8,6 +8,8 @@ #include <stdio.h> #include <string.h>

+#include <linux/compiler.h> + #include "test_signals.h"

int test_init(struct tdescr *td); @@ -76,7 +78,7 @@ static __always_inline bool get_current_context(struct tdescr *td, */ for (i = 0; i < td->live_sz; i++) { uc[i] = 0; - __asm__ ("" : "=r" (uc[i]) : "0" (uc[i])); + OPTIMIZER_HIDE_VAR(uc[0]); }

td->live_uc = dest_uc;