From: Mark Brown <broonie@kernel.org> To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Shuah Khan <shuah@kernel.org> Cc: linux-arm-kernel@lists.infradead.org, linux-kselftest@vger.kernel.org, Mark Brown <broonie@kernel.org> Subject: [PATCH] kselftest/arm64: Exit streaming mode after collecting signal context Date: Wed, 28 Jun 2023 23:52:58 +0100 [thread overview] Message-ID: <20230628-arm64-signal-memcpy-fix-v1-1-db3e0300829e@kernel.org> (raw) 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 | 28 +++++++++++++++++++++- 1 file changed, 27 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..db28409fd44b 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -60,13 +60,28 @@ 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++) { + asm volatile("nop" + : "+m" (*dest_uc) + : + : "memory"); + uc[i] = 0; + } + td->live_uc = dest_uc; /* * Grab ucontext_t triggering a SIGTRAP. @@ -103,6 +118,17 @@ 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 --- base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1 change-id: 20230628-arm64-signal-memcpy-fix-7de3b3c8fa10 Best regards, -- Mark Brown <broonie@kernel.org>
WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@kernel.org> To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Shuah Khan <shuah@kernel.org> Cc: linux-arm-kernel@lists.infradead.org, linux-kselftest@vger.kernel.org, Mark Brown <broonie@kernel.org> Subject: [PATCH] kselftest/arm64: Exit streaming mode after collecting signal context Date: Wed, 28 Jun 2023 23:52:58 +0100 [thread overview] Message-ID: <20230628-arm64-signal-memcpy-fix-v1-1-db3e0300829e@kernel.org> (raw) 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 | 28 +++++++++++++++++++++- 1 file changed, 27 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..db28409fd44b 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -60,13 +60,28 @@ 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++) { + asm volatile("nop" + : "+m" (*dest_uc) + : + : "memory"); + uc[i] = 0; + } + td->live_uc = dest_uc; /* * Grab ucontext_t triggering a SIGTRAP. @@ -103,6 +118,17 @@ 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 --- base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1 change-id: 20230628-arm64-signal-memcpy-fix-7de3b3c8fa10 Best regards, -- Mark Brown <broonie@kernel.org> _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next reply other threads:[~2023-06-28 22:53 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-06-28 22:52 Mark Brown [this message] 2023-06-28 22:52 ` [PATCH] kselftest/arm64: Exit streaming mode after collecting signal context Mark Brown
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20230628-arm64-signal-memcpy-fix-v1-1-db3e0300829e@kernel.org \ --to=broonie@kernel.org \ --cc=catalin.marinas@arm.com \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-kselftest@vger.kernel.org \ --cc=shuah@kernel.org \ --cc=will@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.