diff mbox series

[v5,3/9] x86: vdso: Expose sigreturn address on vdso to the kernel

Message ID 20200810232636.1415588-4-krisman@collabora.com
State New
Headers show
Series Syscall User Dispatch | expand

Commit Message

Gabriel Krisman Bertazi Aug. 10, 2020, 11:26 p.m. UTC
Syscall user redirection requires the signal trampoline code to not be
captured, in order to support returning with a locked selector while
avoiding recursion back into the signal handler.  For ia-32, which has
the trampoline in the vDSO, expose the entry points to the kernel, such
that it can avoid dispatching syscalls from that region to userspace.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 arch/x86/entry/vdso/vdso2c.c           |  2 ++
 arch/x86/entry/vdso/vdso32/sigreturn.S |  2 ++
 arch/x86/entry/vdso/vma.c              | 15 +++++++++++++++
 arch/x86/include/asm/elf.h             |  1 +
 arch/x86/include/asm/vdso.h            |  2 ++
 5 files changed, 22 insertions(+)

Comments

Andy Lutomirski Aug. 11, 2020, 6:50 p.m. UTC | #1
On Mon, Aug 10, 2020 at 4:26 PM Gabriel Krisman Bertazi
<krisman@collabora.com> wrote:
>
> Syscall user redirection requires the signal trampoline code to not be
> captured, in order to support returning with a locked selector while
> avoiding recursion back into the signal handler.  For ia-32, which has
> the trampoline in the vDSO, expose the entry points to the kernel, such
> that it can avoid dispatching syscalls from that region to userspace.

Almost looks good.

> +int arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)

If you make that bool instead of int, feel free to add:

Acked-by: Andy Lutomirski <luto@kernel.org>
diff mbox series

Patch

diff --git a/arch/x86/entry/vdso/vdso2c.c b/arch/x86/entry/vdso/vdso2c.c
index 7380908045c7..2d0f3d8bcc25 100644
--- a/arch/x86/entry/vdso/vdso2c.c
+++ b/arch/x86/entry/vdso/vdso2c.c
@@ -101,6 +101,8 @@  struct vdso_sym required_syms[] = {
 	{"__kernel_sigreturn", true},
 	{"__kernel_rt_sigreturn", true},
 	{"int80_landing_pad", true},
+	{"vdso32_rt_sigreturn_landing_pad", true},
+	{"vdso32_sigreturn_landing_pad", true},
 };
 
 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
diff --git a/arch/x86/entry/vdso/vdso32/sigreturn.S b/arch/x86/entry/vdso/vdso32/sigreturn.S
index c3233ee98a6b..1bd068f72d4c 100644
--- a/arch/x86/entry/vdso/vdso32/sigreturn.S
+++ b/arch/x86/entry/vdso/vdso32/sigreturn.S
@@ -18,6 +18,7 @@  __kernel_sigreturn:
 	movl $__NR_sigreturn, %eax
 	SYSCALL_ENTER_KERNEL
 .LEND_sigreturn:
+SYM_INNER_LABEL(vdso32_sigreturn_landing_pad, SYM_L_GLOBAL)
 	nop
 	.size __kernel_sigreturn,.-.LSTART_sigreturn
 
@@ -29,6 +30,7 @@  __kernel_rt_sigreturn:
 	movl $__NR_rt_sigreturn, %eax
 	SYSCALL_ENTER_KERNEL
 .LEND_rt_sigreturn:
+SYM_INNER_LABEL(vdso32_rt_sigreturn_landing_pad, SYM_L_GLOBAL)
 	nop
 	.size __kernel_rt_sigreturn,.-.LSTART_rt_sigreturn
 	.previous
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 9185cb1d13b9..1828ed2f4a5f 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -436,6 +436,21 @@  int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 }
 #endif
 
+int arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
+{
+#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
+	const struct vdso_image *image = current->mm->context.vdso_image;
+	unsigned long vdso = (unsigned long) current->mm->context.vdso;
+
+	if (in_ia32_syscall() && image == &vdso_image_32) {
+		if (regs->ip == vdso + image->sym_vdso32_sigreturn_landing_pad ||
+		    regs->ip == vdso + image->sym_vdso32_rt_sigreturn_landing_pad)
+			return 1;
+	}
+#endif
+	return 0;
+}
+
 #ifdef CONFIG_X86_64
 static __init int vdso_setup(char *s)
 {
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 452beed7892b..b8fd74f7207d 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -385,6 +385,7 @@  extern int arch_setup_additional_pages(struct linux_binprm *bprm,
 				       int uses_interp);
 extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
 					      int uses_interp);
+extern int arch_syscall_is_vdso_sigreturn(struct pt_regs *regs);
 #define compat_arch_setup_additional_pages compat_arch_setup_additional_pages
 
 /* Do not change the values. See get_align_mask() */
diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index bbcdc7b8f963..589f489dd375 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -27,6 +27,8 @@  struct vdso_image {
 	long sym___kernel_rt_sigreturn;
 	long sym___kernel_vsyscall;
 	long sym_int80_landing_pad;
+	long sym_vdso32_sigreturn_landing_pad;
+	long sym_vdso32_rt_sigreturn_landing_pad;
 };
 
 #ifdef CONFIG_X86_64