Author: kib Date: Tue Mar 20 17:43:50 2018 New Revision: 331252 URL: https://svnweb.freebsd.org/changeset/base/331252
Log: Provide KPI for handling of rw/ro kernel text. This is a pure syntax patch to create an interface to enable and later restore write access to the kernel text and other read-only mapped regions. It is in line with e.g. vm_fault_disable_pagefaults() by allowing the nesting. Discussed with: Peter Lei <peter....@ieee.org> Reviewed by: jtl Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D14768 Modified: head/sys/amd64/amd64/db_interface.c head/sys/amd64/amd64/gdb_machdep.c head/sys/amd64/amd64/machdep.c head/sys/amd64/include/md_var.h Modified: head/sys/amd64/amd64/db_interface.c ============================================================================== --- head/sys/amd64/amd64/db_interface.c Tue Mar 20 17:41:54 2018 (r331251) +++ head/sys/amd64/amd64/db_interface.c Tue Mar 20 17:43:50 2018 (r331252) @@ -37,6 +37,7 @@ __FBSDID("$FreeBSD$"); #include <sys/pcpu.h> #include <machine/cpufunc.h> +#include <machine/md_var.h> #include <machine/specialreg.h> #include <ddb/ddb.h> @@ -75,19 +76,19 @@ db_write_bytes(vm_offset_t addr, size_t size, char *da jmp_buf jb; void *prev_jb; char *dst; - u_long cr0save; + bool old_wp; int ret; - cr0save = rcr0(); + old_wp = false; prev_jb = kdb_jmpbuf(jb); ret = setjmp(jb); if (ret == 0) { - load_cr0(cr0save & ~CR0_WP); + old_wp = disable_wp(); dst = (char *)addr; while (size-- > 0) *dst++ = *data++; } - load_cr0(cr0save); + restore_wp(old_wp); (void)kdb_jmpbuf(prev_jb); return (ret); } Modified: head/sys/amd64/amd64/gdb_machdep.c ============================================================================== --- head/sys/amd64/amd64/gdb_machdep.c Tue Mar 20 17:41:54 2018 (r331251) +++ head/sys/amd64/amd64/gdb_machdep.c Tue Mar 20 17:43:50 2018 (r331252) @@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$"); #include <machine/cpufunc.h> #include <machine/frame.h> #include <machine/gdb_machdep.h> +#include <machine/md_var.h> #include <machine/pcb.h> #include <machine/psl.h> #include <machine/reg.h> @@ -127,17 +128,14 @@ gdb_cpu_signal(int type, int code) void * gdb_begin_write(void) { - u_long cr0save; - cr0save = rcr0(); - load_cr0(cr0save & ~CR0_WP); - return ((void *)cr0save); + return (disable_wp() ? &gdb_begin_write : NULL); } void gdb_end_write(void *arg) { - load_cr0((u_long)arg); + restore_wp(arg != NULL); } Modified: head/sys/amd64/amd64/machdep.c ============================================================================== --- head/sys/amd64/amd64/machdep.c Tue Mar 20 17:41:54 2018 (r331251) +++ head/sys/amd64/amd64/machdep.c Tue Mar 20 17:43:50 2018 (r331252) @@ -2597,6 +2597,31 @@ clear_pcb_flags(struct pcb *pcb, const u_int flags) : "cc", "memory"); } +/* + * Enable and restore kernel text write permissions. + * Callers must ensure that disable_wp()/restore_wp() are executed + * without rescheduling on the same core. + */ +bool +disable_wp(void) +{ + u_int cr0; + + cr0 = rcr0(); + if ((cr0 & CR0_WP) == 0) + return (false); + load_cr0(cr0 & ~CR0_WP); + return (true); +} + +void +restore_wp(bool old_wp) +{ + + if (old_wp) + load_cr0(rcr0() | CR0_WP); +} + #ifdef KDB /* Modified: head/sys/amd64/include/md_var.h ============================================================================== --- head/sys/amd64/include/md_var.h Tue Mar 20 17:41:54 2018 (r331251) +++ head/sys/amd64/include/md_var.h Tue Mar 20 17:43:50 2018 (r331252) @@ -53,6 +53,8 @@ void amd64_conf_fast_syscall(void); void amd64_db_resume_dbreg(void); void amd64_lower_shared_page(struct sysentvec *); void amd64_syscall(struct thread *td, int traced); +bool disable_wp(void); +void restore_wp(bool old_wp); void doreti_iret(void) __asm(__STRING(doreti_iret)); void doreti_iret_fault(void) __asm(__STRING(doreti_iret_fault)); void ld_ds(void) __asm(__STRING(ld_ds)); _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
