um: switch to regset API and depend on XSTATE

The PTRACE_GETREGSET API has now existed since Linux 2.6.33. The XSAVE
CPU feature should also be sufficiently common to be able to rely on it.

With this, define our internal FP state to be the hosts XSAVE data. Add
discovery for the hosts XSAVE size and place the FP registers at the end
of task_struct so that we can adjust the size at runtime.

Next we can implement the regset API on top and update the signal
handling as well as ptrace APIs to use them. Also switch coredump
creation to use the regset API and finally set HAVE_ARCH_TRACEHOOK.

This considerably improves the signal frames. Previously they might not
have contained all the registers (i386) and also did not have the
sizes and magic values set to the correct values to permit userspace to
decode the frame.

As a side effect, this will permit UML to run on hosts with newer CPU
extensions (such as AMX) that need even more register state.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20241023094120.4083426-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

4 files changed, 7 insertions, 15 deletions

diff --git a/arch/x86/um/shared/sysdep/ptrace.h b/arch/x86/um/shared/sysdep/ptrace.h
index 6ca4ecabc55b..2dd4ca6713f8 100644
--- a/arch/x86/um/shared/sysdep/ptrace.h
+++ b/arch/x86/um/shared/sysdep/ptrace.h
@@ -56,12 +56,16 @@ struct syscall_args {
 				     UPT_SYSCALL_ARG5(r),	 \
 				     UPT_SYSCALL_ARG6(r) } } )
 
+extern unsigned long host_fp_size;
+
 struct uml_pt_regs {
 	unsigned long gp[MAX_REG_NR];
-	unsigned long fp[MAX_FP_NR];
 	struct faultinfo faultinfo;
 	long syscall;
 	int is_user;
+
+	/* Dynamically sized FP registers (holds an XSTATE) */
+	unsigned long fp[];
 };
 
 #define EMPTY_UML_PT_REGS { }
@@ -72,4 +76,6 @@ struct uml_pt_regs {
 
 extern int user_context(unsigned long sp);
 
+extern int arch_init_registers(int pid);
+
 #endif /* __SYSDEP_X86_PTRACE_H */
diff --git a/arch/x86/um/shared/sysdep/ptrace_32.h b/arch/x86/um/shared/sysdep/ptrace_32.h
index 0c4989842fbe..2392470cac4d 100644
--- a/arch/x86/um/shared/sysdep/ptrace_32.h
+++ b/arch/x86/um/shared/sysdep/ptrace_32.h
@@ -6,8 +6,6 @@
 #ifndef __SYSDEP_I386_PTRACE_H
 #define __SYSDEP_I386_PTRACE_H
 
-#define MAX_FP_NR HOST_FPX_SIZE
-
 #define UPT_SYSCALL_ARG1(r) UPT_BX(r)
 #define UPT_SYSCALL_ARG2(r) UPT_CX(r)
 #define UPT_SYSCALL_ARG3(r) UPT_DX(r)
@@ -15,6 +13,4 @@
 #define UPT_SYSCALL_ARG5(r) UPT_DI(r)
 #define UPT_SYSCALL_ARG6(r) UPT_BP(r)
 
-extern void arch_init_registers(int pid);
-
 #endif
diff --git a/arch/x86/um/shared/sysdep/ptrace_64.h b/arch/x86/um/shared/sysdep/ptrace_64.h
index 0dc223aa1c2d..e73573ac871f 100644
--- a/arch/x86/um/shared/sysdep/ptrace_64.h
+++ b/arch/x86/um/shared/sysdep/ptrace_64.h
@@ -8,8 +8,6 @@
 #ifndef __SYSDEP_X86_64_PTRACE_H
 #define __SYSDEP_X86_64_PTRACE_H
 
-#define MAX_FP_NR HOST_FP_SIZE
-
 #define REGS_R8(r) ((r)[HOST_R8])
 #define REGS_R9(r) ((r)[HOST_R9])
 #define REGS_R10(r) ((r)[HOST_R10])
@@ -57,6 +55,4 @@
 #define UPT_SYSCALL_ARG5(r) UPT_R8(r)
 #define UPT_SYSCALL_ARG6(r) UPT_R9(r)
 
-extern void arch_init_registers(int pid);
-
 #endif
diff --git a/arch/x86/um/shared/sysdep/ptrace_user.h b/arch/x86/um/shared/sysdep/ptrace_user.h
index 1d1a824fa652..98da23120538 100644
--- a/arch/x86/um/shared/sysdep/ptrace_user.h
+++ b/arch/x86/um/shared/sysdep/ptrace_user.h
@@ -11,12 +11,6 @@
 #define REGS_IP_INDEX HOST_IP
 #define REGS_SP_INDEX HOST_SP
 
-#ifdef __i386__
-#define FP_SIZE ((HOST_FPX_SIZE > HOST_FP_SIZE) ? HOST_FPX_SIZE : HOST_FP_SIZE)
-#else
-#define FP_SIZE HOST_FP_SIZE
-#endif
-
 /*
  * glibc before 2.27 does not include PTRACE_SYSEMU_SINGLESTEP in its enum,
  * ensure we have a definition by (re-)defining it here.