x86, math-emu: fix init_fpu for task != current (ab9e1858) · Commits · 戴 / test

Impact: fix math-emu related crash while using GDB/ptrace init_fpu() calls finit to initialize a task's xstate, while finit always works on the current task. If we use PTRACE_GETFPREGS on another process and both processes did not already use floating point, we get a null pointer exception in finit. This patch creates a new function finit_task that takes a task_struct parameter. finit becomes a wrapper that simply calls finit_task with current. On the plus side this avoids many calls to get_current which would each resolve to an inline assembler mov instruction. An empty finit_task has been added to i387.h to avoid linker errors in case the compiler still emits the call in init_fpu when CONFIG_MATH_EMULATION is not defined. The declaration of finit in i387.h has been removed as the remaining code using this function gets its prototype from fpu_proto.h. Signed-off-by:

Daniel Glöckner <dg@emlix.com> Cc: Suresh Siddha <suresh.b.siddha@intel.com> Cc: "Pallipadi Venkatesh" <venkatesh.pallipadi@intel.com> Cc: Arjan van de Ven <arjan@infradead.org> Cc: Bill Metzenthen <billm@melbpc.org.au> LKML-Reference: <E1Lew31-0004il-Fg@mailer.emlix.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/i387.h

+7 −1

Original line number	Diff line number	Diff line
		@@ -172,7 +172,13 @@ static inline void __save_init_fpu(struct task_struct *tsk)

		#else /* CONFIG_X86_32 */

		extern void finit(void);
		#ifdef CONFIG_MATH_EMULATION
		extern void finit_task(struct task_struct *tsk);
		#else
		static inline void finit_task(struct task_struct *tsk)
		{
		}
		#endif

		static inline void tolerant_fwait(void)
		{

arch/x86/kernel/i387.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -136,7 +136,7 @@ int init_fpu(struct task_struct *tsk)
		#ifdef CONFIG_X86_32
		if (!HAVE_HWFP) {
		memset(tsk->thread.xstate, 0, xstate_size);
		finit();
		finit_task(tsk);
		set_stopped_child_used_math(tsk);
		return 0;
		}

arch/x86/math-emu/fpu_aux.c

+20 −11

Original line number	Diff line number	Diff line
		@@ -30,20 +30,29 @@ static void fclex(void)
		}

		/* Needs to be externally visible */
		void finit(void)
		void finit_task(struct task_struct *tsk)
		{
		control_word = 0x037f;
		partial_status = 0;
		top = 0; /* We don't keep top in the status word internally. */
		fpu_tag_word = 0xffff;
		struct i387_soft_struct *soft = &tsk->thread.xstate->soft;
		struct address oaddr, iaddr;
		soft->cwd = 0x037f;
		soft->swd = 0;
		soft->ftop = 0; /* We don't keep top in the status word internally. */
		soft->twd = 0xffff;
		/* The behaviour is different from that detailed in
		Section 15.1.6 of the Intel manual */
		operand_address.offset = 0;
		operand_address.selector = 0;
		instruction_address.offset = 0;
		instruction_address.selector = 0;
		instruction_address.opcode = 0;
		no_ip_update = 1;
		oaddr = (struct address *)&soft->foo;
		oaddr->offset = 0;
		oaddr->selector = 0;
		iaddr = (struct address *)&soft->fip;
		iaddr->offset = 0;
		iaddr->selector = 0;
		iaddr->opcode = 0;
		soft->no_update = 1;
		}

		void finit(void)
		{
		finit_task(current);
		}

		/*

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