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From 5c537b3d0cf8c393dad2e61d49aade68f3af1401 Mon Sep 17 00:00:00 2001
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From: dann frazier <dann.frazier@canonical.com>
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Date: Tue, 6 Sep 2022 09:28:22 -0600
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Subject: [PATCH 06/13] shim: Flush the memory region from i-cache before
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execution
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We've seen crashes in early GRUB code on an ARM Cortex-A72-based
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platform that point at seemingly harmless instructions. Flushing
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the i-cache of those instructions prior to executing has been
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shown to avoid the problem, which has parallels with this story:
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https://www.mail-archive.com/osv-dev@googlegroups.com/msg06203.html
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Add a cache flushing utility function and provide an implementation
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using a GCC intrinsic. This will need to be extended to support other
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compilers. Note that this intrinsic is a no-op for x86 platforms.
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This fixes issue #498.
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Signed-off-by: dann frazier <dann.frazier@canonical.com>
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---
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pe.c | 3 +++
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include/compiler.h | 6 ++++++
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2 files changed, 9 insertions(+)
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diff --git a/pe.c b/pe.c
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index ba3e2bbc444..f94530a20c0 100644
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--- a/pe.c
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+++ b/pe.c
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@@ -1196,6 +1196,9 @@ handle_image (void *data, unsigned int datasize,
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CopyMem(buffer, data, context.SizeOfHeaders);
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+ /* Flush the instruction cache for the region holding the image */
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+ cache_invalidate(buffer, buffer + context.ImageSize);
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+
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*entry_point = ImageAddress(buffer, context.ImageSize, context.EntryPoint);
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if (!*entry_point) {
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perror(L"Entry point is invalid\n");
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diff --git a/include/compiler.h b/include/compiler.h
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index b4bf10319ee..b0d595f32c2 100644
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--- a/include/compiler.h
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+++ b/include/compiler.h
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@@ -192,5 +192,11 @@
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*/
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#define unreachable() __builtin_unreachable()
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+#if defined(__GNUC__)
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+#define cache_invalidate(begin, end) __builtin___clear_cache(begin, end)
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+#else /* __GNUC__ */
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+#error shim has no cache_invalidate() implementation for this compiler
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+#endif /* __GNUC__ */
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+
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#endif /* !COMPILER_H_ */
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// vim:fenc=utf-8:tw=75:et
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--
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2.37.1
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