linux-kernel - [PATCH 4/4] powerpc/vdso: Refactor error handling

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Message-ID: <20240807124103.85644-4-mpe@ellerman.id.au>
Date: Wed,  7 Aug 2024 22:41:03 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: <linux-mm@...ck.org>
Cc: <linuxppc-dev@...ts.ozlabs.org>,
	torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org,
	christophe.leroy@...roup.eu,
	jeffxu@...omium.org,
	jeffxu@...gle.com,
	Liam.Howlett@...cle.com,
	linux-kernel@...r.kernel.org,
	npiggin@...il.com,
	oliver.sang@...el.com,
	pedro.falcato@...il.com
Subject: [PATCH 4/4] powerpc/vdso: Refactor error handling

Linus noticed that the error handling in __arch_setup_additional_pages()
fails to clear the mm VDSO pointer if _install_special_mapping()
fails. In practice there should be no actual bug, because if there's an
error the VDSO pointer is cleared later in arch_setup_additional_pages().

However it's no longer necessary to set the pointer before installing
the mapping. Commit c1bab64360e6 ("powerpc/vdso: Move to
_install_special_mapping() and remove arch_vma_name()") reworked the
code so that the VMA name comes from the vm_special_mapping.name, rather
than relying on arch_vma_name().

So rework the code to only set the VDSO pointer once the mappings have
been installed correctly, and remove the stale comment.

Depends-on: c1bab64360e6 ("powerpc/vdso: Move to _install_special_mapping() and remove arch_vma_name()")
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
---
 arch/powerpc/kernel/vdso.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 220a76cae7c1..ee4b9d676cff 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -214,13 +214,6 @@ static int __arch_setup_additional_pages(struct linux_binprm *bprm, int uses_int
 	/* Add required alignment. */
 	vdso_base = ALIGN(vdso_base, VDSO_ALIGNMENT);
 
-	/*
-	 * Put vDSO base into mm struct. We need to do this before calling
-	 * install_special_mapping or the perf counter mmap tracking code
-	 * will fail to recognise it as a vDSO.
-	 */
-	mm->context.vdso = (void __user *)vdso_base + vvar_size;
-
 	vma = _install_special_mapping(mm, vdso_base, vvar_size,
 				       VM_READ | VM_MAYREAD | VM_IO |
 				       VM_DONTDUMP | VM_PFNMAP, &vvar_spec);
@@ -240,10 +233,15 @@ static int __arch_setup_additional_pages(struct linux_binprm *bprm, int uses_int
 	vma = _install_special_mapping(mm, vdso_base + vvar_size, vdso_size,
 				       VM_READ | VM_EXEC | VM_MAYREAD |
 				       VM_MAYWRITE | VM_MAYEXEC, vdso_spec);
-	if (IS_ERR(vma))
+	if (IS_ERR(vma)) {
 		do_munmap(mm, vdso_base, vvar_size, NULL);
+		return PTR_ERR(vma);
+	}
 
-	return PTR_ERR_OR_ZERO(vma);
+	// Now that the mappings are in place, set the mm VDSO pointer
+	mm->context.vdso = (void __user *)vdso_base + vvar_size;
+
+	return 0;
 }
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
@@ -257,8 +255,6 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 		return -EINTR;
 
 	rc = __arch_setup_additional_pages(bprm, uses_interp);
-	if (rc)
-		mm->context.vdso = NULL;
 
 	mmap_write_unlock(mm);
 	return rc;
-- 
2.45.2