diff mbox series

[RESUBMIT,bpf-next,1/2] mm: Fix copy_from_user_nofault().

Message ID 20230329193931.320642-2-dev@der-flo.net (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Fix copy_from_user_nofault() | expand

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Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 20 this patch: 20
netdev/cc_maintainers warning 3 maintainers not CCed: linux-hardening@vger.kernel.org akpm@linux-foundation.org linux-mm@kvack.org
netdev/build_clang success Errors and warnings before: 18 this patch: 18
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
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netdev/checkpatch warning WARNING: Reported-by: should be immediately followed by Link: with a URL to the report
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-next-PR success PR summary
bpf/vmtest-bpf-next-VM_Test-1 success Logs for ${{ matrix.test }} on ${{ matrix.arch }} with ${{ matrix.toolchain_full }}
bpf/vmtest-bpf-next-VM_Test-2 success Logs for ShellCheck
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Commit Message

Florian Lehner March 29, 2023, 7:39 p.m. UTC 
From: Alexei Starovoitov <ast@kernel.org>

There are several issues with copy_from_user_nofault():

- access_ok() is designed for user context only and for that reason
it has WARN_ON_IN_IRQ() which triggers when bpf, kprobe, eprobe
and perf on ppc are calling it from irq.

- it's missing nmi_uaccess_okay() which is a nop on all architectures
except x86 where it's required.
The comment in arch/x86/mm/tlb.c explains the details why it's necessary.
Calling copy_from_user_nofault() from bpf, [ke]probe without this check is not safe.

- __copy_from_user_inatomic() under CONFIG_HARDENED_USERCOPY is calling
check_object_size()->__check_object_size()->check_heap_object()->find_vmap_area()->spin_lock()
which is not safe to do from bpf, [ke]probe and perf due to potential deadlock.

Fix all three issues. At the end the copy_from_user_nofault() becomes
equivalent to copy_from_user_nmi() from safety point of view with
a difference in the return value.

Reported-by: Hsin-Wei Hung <hsinweih@uci.edu>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Hsin-Wei Hung <hsinweih@uci.edu>
Tested-by: Florian Lehner <dev@der-flo.net>
---
 mm/maccess.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)
diff mbox series

Patch

diff --git a/mm/maccess.c b/mm/maccess.c
index 074f6b086671..6ee9b337c501 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -5,6 +5,7 @@ 
 #include <linux/export.h>
 #include <linux/mm.h>
 #include <linux/uaccess.h>
+#include <asm/tlb.h>
 
 bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
 		size_t size)
@@ -113,11 +114,18 @@  long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
 long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
 {
 	long ret = -EFAULT;
-	if (access_ok(src, size)) {
-		pagefault_disable();
-		ret = __copy_from_user_inatomic(dst, src, size);
-		pagefault_enable();
-	}
+
+	if (!__access_ok(src, size))
+		return ret;
+
+	if (!nmi_uaccess_okay())
+		return ret;
+
+	pagefault_disable();
+	instrument_copy_from_user_before(dst, src, size);
+	ret = raw_copy_from_user(dst, src, size);
+	instrument_copy_from_user_after(dst, src, size, ret);
+	pagefault_enable();
 
 	if (ret)
 		return -EFAULT;