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-rw-r--r--target/linux/patches/6.6.32/armnommu-fix-thread-registers.patch57
1 files changed, 57 insertions, 0 deletions
diff --git a/target/linux/patches/6.6.32/armnommu-fix-thread-registers.patch b/target/linux/patches/6.6.32/armnommu-fix-thread-registers.patch
new file mode 100644
index 000000000..8ab2196dc
--- /dev/null
+++ b/target/linux/patches/6.6.32/armnommu-fix-thread-registers.patch
@@ -0,0 +1,57 @@
+From 1410ebe685f13c1699a16bf147ae1332e7fd1983 Mon Sep 17 00:00:00 2001
+From: Greg Ungerer <gerg@kernel.org>
+Date: Thu, 20 Apr 2023 09:52:08 +1000
+Subject: [PATCH] ARM: start_thread: restore registers on ELF load for noMMU
+
+The binfmt_elf-fdpic loader is capable of loading constant displacement
+ELF format binaries (like those compiled -pie) on noMMU systems as well
+as elf-fdpic format binaries. The traditional ELF loader cannot be
+enabled on noMMU systems.
+
+Commit 5e588114329c ("ARM: start_thread(): don't always clear all regs")
+fixed the start_thread() code so that it maintains the required
+elf-fdpic registers through to the new process, but it only does that if
+current has its personality FDPIC_FUNCPTRS bit set. That is true for
+elf-fdpic format binaries but will not be true for non-fdpic ELF
+binaries.
+
+Modify the test of the FDPIC_FUNCPTRS personality bit to also carry out
+the register restore if this is a noMMU system. This is not perfect,
+since it will also preserve these registers on noMMU systems for all
+binary format types (could be flat format for example). That won't break
+anything, but it is potentially leaking some information into the new
+process. But for the noMMU case we need those start time registers set to
+be able to finalize the runtime loading of the -pie style ELF binary
+(carry out its segment and dynamic relocation processing).
+
+Unfortunately the FDPIC_FUNCPTRS flag cannot just be enabled for all
+elf-fdpic loaded binaries. That personality bit is used for other things
+like the controlling the changed behavior for signal handling.
+
+There is no change in behavior for normal ELF loading on MMU systems.
+A -pie style ELF binary built for noMMU systems can be load and run using
+the usual ELF loader on an MMU system (elf-fdpic loader not required in
+this case).
+
+Signed-off-by: Greg Ungerer <gerg@kernel.org>
+---
+ arch/arm/include/asm/processor.h | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
+index 326864f79d18..5074cc3ae4e1 100644
+--- a/arch/arm/include/asm/processor.h
++++ b/arch/arm/include/asm/processor.h
+@@ -60,7 +60,8 @@ static inline void arch_thread_struct_whitelist(unsigned long *offset,
+ } \
+ memset(regs->uregs, 0, sizeof(regs->uregs)); \
+ if (IS_ENABLED(CONFIG_BINFMT_ELF_FDPIC) && \
+- current->personality & FDPIC_FUNCPTRS) { \
++ ((! IS_ENABLED(CONFIG_MMU)) || \
++ current->personality & FDPIC_FUNCPTRS)) { \
+ regs->ARM_r7 = r7; \
+ regs->ARM_r8 = r8; \
+ regs->ARM_r9 = r9; \
+--
+2.25.1
+