[PATCH v7 1/7] x86: vdso: Expose sigreturn address on vdso to the kernel

Gabriel Krisman Bertazi
2020-11-18T03:29:26Z

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@kernel.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

---
Changes since V5
- Change return address to bool (Andy)
---
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 | 2 ++
arch/x86/include/asm/vdso.h | 2 ++
5 files changed, 23 insertions(+)

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 50e5d3a2e70a..de60cd37070b 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

+bool 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 true;
+ }
+#endif
+ return false;
+}
+
#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 44a9b9940535..66bdfe838d61 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -388,6 +388,8 @@ extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
compat_arch_setup_additional_pages(bprm, interpreter, \
(ex->e_machine == EM_X86_64))

+extern bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs);
+
/* Do not change the values. See get_align_mask() */
enum align_flags {
ALIGN_VA_32 = BIT(0),
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
--
2.29.2