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([71.212.157.132]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-794e1fc9db6sm740724b3a.66.2025.10.08.15.00.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Oct 2025 15:00:00 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Cc: qemu-arm@nongnu.org, Pierrick Bouvier Subject: [PATCH v7 69/73] linux-user/aarch64: Generate GCS signal records Date: Wed, 8 Oct 2025 14:56:09 -0700 Message-ID: <20251008215613.300150-70-richard.henderson@linaro.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251008215613.300150-1-richard.henderson@linaro.org> References: <20251008215613.300150-1-richard.henderson@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::42b; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x42b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Here we must push and pop a cap on the GCS stack as well as the gcs record on the normal stack. Reviewed-by: Pierrick Bouvier Signed-off-by: Richard Henderson --- linux-user/aarch64/signal.c | 138 ++++++++++++++++++++++++++++++++++-- 1 file changed, 132 insertions(+), 6 deletions(-) diff --git a/linux-user/aarch64/signal.c b/linux-user/aarch64/signal.c index ef97be3ac7..f7edfa249e 100644 --- a/linux-user/aarch64/signal.c +++ b/linux-user/aarch64/signal.c @@ -22,6 +22,7 @@ #include "signal-common.h" #include "linux-user/trace.h" #include "target/arm/cpu-features.h" +#include "gcs-internal.h" struct target_sigcontext { uint64_t fault_address; @@ -152,6 +153,16 @@ struct target_zt_context { QEMU_BUILD_BUG_ON(TARGET_ZT_SIG_REG_BYTES != \ sizeof_field(CPUARMState, za_state.zt0)); +#define TARGET_GCS_MAGIC 0x47435300 +#define GCS_SIGNAL_CAP(X) ((X) & TARGET_PAGE_MASK) + +struct target_gcs_context { + struct target_aarch64_ctx head; + uint64_t gcspr; + uint64_t features_enabled; + uint64_t reserved; +}; + struct target_rt_sigframe { struct target_siginfo info; struct target_ucontext uc; @@ -322,6 +333,35 @@ static void target_setup_zt_record(struct target_zt_context *zt, } } +static bool target_setup_gcs_record(struct target_gcs_context *ctx, + CPUARMState *env, uint64_t return_addr) +{ + uint64_t mode = gcs_get_el0_mode(env); + uint64_t gcspr = env->cp15.gcspr_el[0]; + + if (mode & PR_SHADOW_STACK_ENABLE) { + /* Push a cap for the signal frame. */ + gcspr -= 8; + if (put_user_u64(GCS_SIGNAL_CAP(gcspr), gcspr)) { + return false; + } + + /* Push a gcs entry for the trampoline. */ + if (put_user_u64(return_addr, gcspr - 8)) { + return false; + } + env->cp15.gcspr_el[0] = gcspr - 8; + } + + __put_user(TARGET_GCS_MAGIC, &ctx->head.magic); + __put_user(sizeof(*ctx), &ctx->head.size); + __put_user(gcspr, &ctx->gcspr); + __put_user(mode, &ctx->features_enabled); + __put_user(0, &ctx->reserved); + + return true; +} + static void target_restore_general_frame(CPUARMState *env, struct target_rt_sigframe *sf) { @@ -502,6 +542,64 @@ static bool target_restore_zt_record(CPUARMState *env, return true; } +static bool target_restore_gcs_record(CPUARMState *env, + struct target_gcs_context *ctx, + bool *rebuild_hflags) +{ + TaskState *ts = get_task_state(env_cpu(env)); + uint64_t cur_mode = gcs_get_el0_mode(env); + uint64_t new_mode, gcspr; + + __get_user(new_mode, &ctx->features_enabled); + __get_user(gcspr, &ctx->gcspr); + + /* + * The kernel pushes the value through the hw register: + * write_sysreg_s(gcspr, SYS_GCSPR_EL0) in restore_gcs_context, + * then read_sysreg_s(SYS_GCSPR_EL0) in gcs_restore_signal. + * Since the bottom 3 bits are RES0, this can (CONSTRAINED UNPREDICTABLE) + * force align the value. Mirror the choice from gcspr_write(). + */ + gcspr &= ~7; + + if (new_mode & ~(PR_SHADOW_STACK_ENABLE | + PR_SHADOW_STACK_WRITE | + PR_SHADOW_STACK_PUSH)) { + return false; + } + if ((new_mode ^ cur_mode) & ts->gcs_el0_locked) { + return false; + } + if (new_mode & ~cur_mode & PR_SHADOW_STACK_ENABLE) { + return false; + } + + if (new_mode & PR_SHADOW_STACK_ENABLE) { + uint64_t cap; + + /* Pop and clear the signal cap. */ + if (get_user_u64(cap, gcspr)) { + return false; + } + if (cap != GCS_SIGNAL_CAP(gcspr)) { + return false; + } + if (put_user_u64(0, gcspr)) { + return false; + } + gcspr += 8; + } else { + new_mode = 0; + } + + env->cp15.gcspr_el[0] = gcspr; + if (new_mode != cur_mode) { + *rebuild_hflags = true; + gcs_set_el0_mode(env, new_mode); + } + return true; +} + static int target_restore_sigframe(CPUARMState *env, struct target_rt_sigframe *sf) { @@ -511,8 +609,10 @@ static int target_restore_sigframe(CPUARMState *env, struct target_za_context *za = NULL; struct target_tpidr2_context *tpidr2 = NULL; struct target_zt_context *zt = NULL; + struct target_gcs_context *gcs = NULL; uint64_t extra_datap = 0; bool used_extra = false; + bool rebuild_hflags = false; int sve_size = 0; int za_size = 0; int zt_size = 0; @@ -582,6 +682,15 @@ static int target_restore_sigframe(CPUARMState *env, zt_size = size; break; + case TARGET_GCS_MAGIC: + if (gcs + || size != sizeof(struct target_gcs_context) + || !cpu_isar_feature(aa64_gcs, env_archcpu(env))) { + goto err; + } + gcs = (struct target_gcs_context *)ctx; + break; + case TARGET_EXTRA_MAGIC: if (extra || size != sizeof(struct target_extra_context)) { goto err; @@ -612,6 +721,10 @@ static int target_restore_sigframe(CPUARMState *env, goto err; } + if (gcs && !target_restore_gcs_record(env, gcs, &rebuild_hflags)) { + goto err; + } + /* SVE data, if present, overwrites FPSIMD data. */ if (sve && !target_restore_sve_record(env, sve, sve_size, &svcr)) { goto err; @@ -631,6 +744,9 @@ static int target_restore_sigframe(CPUARMState *env, } if (env->svcr != svcr) { env->svcr = svcr; + rebuild_hflags = true; + } + if (rebuild_hflags) { arm_rebuild_hflags(env); } unlock_user(extra, extra_datap, 0); @@ -701,7 +817,7 @@ static void target_setup_frame(int usig, struct target_sigaction *ka, uc.tuc_mcontext.__reserved), }; int fpsimd_ofs, fr_ofs, sve_ofs = 0, za_ofs = 0, tpidr2_ofs = 0; - int zt_ofs = 0, esr_ofs = 0; + int zt_ofs = 0, esr_ofs = 0, gcs_ofs = 0; int sve_size = 0, za_size = 0, tpidr2_size = 0, zt_size = 0; struct target_rt_sigframe *frame; struct target_rt_frame_record *fr; @@ -720,6 +836,11 @@ static void target_setup_frame(int usig, struct target_sigaction *ka, &layout); } + if (env->cp15.gcspr_el[0]) { + gcs_ofs = alloc_sigframe_space(sizeof(struct target_gcs_context), + &layout); + } + /* SVE state needs saving only if it exists. */ if (cpu_isar_feature(aa64_sve, env_archcpu(env)) || cpu_isar_feature(aa64_sme, env_archcpu(env))) { @@ -779,6 +900,12 @@ static void target_setup_frame(int usig, struct target_sigaction *ka, goto give_sigsegv; } + if (ka->sa_flags & TARGET_SA_RESTORER) { + return_addr = ka->sa_restorer; + } else { + return_addr = default_rt_sigreturn; + } + target_setup_general_frame(frame, env, set); target_setup_fpsimd_record((void *)frame + fpsimd_ofs, env); if (esr_ofs) { @@ -786,6 +913,10 @@ static void target_setup_frame(int usig, struct target_sigaction *ka, /* Leave ESR_EL1 clear while it's not relevant. */ env->cp15.esr_el[1] = 0; } + if (gcs_ofs && + !target_setup_gcs_record((void *)frame + gcs_ofs, env, return_addr)) { + goto give_sigsegv; + } target_setup_end_record((void *)frame + layout.std_end_ofs); if (layout.extra_ofs) { target_setup_extra_record((void *)frame + layout.extra_ofs, @@ -811,11 +942,6 @@ static void target_setup_frame(int usig, struct target_sigaction *ka, __put_user(env->xregs[29], &fr->fp); __put_user(env->xregs[30], &fr->lr); - if (ka->sa_flags & TARGET_SA_RESTORER) { - return_addr = ka->sa_restorer; - } else { - return_addr = default_rt_sigreturn; - } env->xregs[0] = usig; env->xregs[29] = frame_addr + fr_ofs; env->xregs[30] = return_addr; -- 2.43.0