[PATCH AUTOSEL 5.4 12/28] ARM: tegra: Use I/O memcpy to write to IRAM

[Sasha Levin <sashal@kernel.org>]

From: Aaron Kling <webgeek1234@gmail.com>

[ Upstream commit 398e67e0f5ae04b29bcc9cbf342e339fe9d3f6f1 ]

Kasan crashes the kernel trying to check boundaries when using the
normal memcpy.

Signed-off-by: Aaron Kling <webgeek1234@gmail.com>
Link: https://lore.kernel.org/r/20250522-mach-tegra-kasan-v1-1-419041b8addb@gmail.com
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Based on my analysis of this commit, here's my determination:

**Backport Status: YES**

This commit should be backported to stable kernel trees for the
following reasons:

1. **Fixes a real crash/bug**: The commit fixes a KASAN (Kernel Address
   Sanitizer) crash that occurs when using regular `memcpy()` to write
   to IRAM (Internal RAM). This is a functional bug that causes kernel
   crashes when KASAN is enabled.

2. **Small and contained fix**: The change is minimal - it simply
   replaces `memcpy()` with `memcpy_toio()` on line 66 of arch/arm/mach-
   tegra/reset.c. This is a one-line change that doesn't alter any logic
   or introduce new features.

3. **Follows proper I/O memory access patterns**: The fix is technically
   correct. According to the kernel documentation in
   Documentation/driver-api/device-io.rst, I/O memory regions (which
   IRAM is mapped as via `IO_ADDRESS()`) should be accessed using
   I/O-specific functions like `memcpy_toio()` rather than regular
   `memcpy()`. The documentation explicitly states: "Do not use memset
   or memcpy on IO addresses; they are not guaranteed to copy data in
   order."

4. **No architectural changes**: The commit doesn't introduce any
   architectural changes or new functionality. It's purely a bug fix
   that corrects improper memory access.

5. **Minimal risk of regression**: Since this change only affects how
   data is copied to IRAM during the Tegra CPU reset handler
   initialization, and uses the proper kernel API for I/O memory access,
   the risk of introducing new issues is very low.

6. **Platform-specific but important**: While this fix is specific to
   ARM Tegra platforms, it fixes a crash that would affect any Tegra
   system running with KASAN enabled. This is important for developers
   and users who rely on KASAN for debugging.

The fact that `iram_base` is obtained through `IO_ADDRESS()` macro
clearly indicates this is I/O mapped memory that requires I/O-specific
accessors. KASAN correctly identified this misuse and crashed to prevent
potential issues. The fix properly uses `memcpy_toio()` which is
designed for copying to I/O memory regions and won't trigger KASAN
checks for regular memory access.

 arch/arm/mach-tegra/reset.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/mach-tegra/reset.c b/arch/arm/mach-tegra/reset.c
index 76a65df42d10..dce0cb1fdd6f 100644
--- a/arch/arm/mach-tegra/reset.c
+++ b/arch/arm/mach-tegra/reset.c
@@ -63,7 +63,7 @@ static void __init tegra_cpu_reset_handler_enable(void)
 	BUG_ON(is_enabled);
 	BUG_ON(tegra_cpu_reset_handler_size > TEGRA_IRAM_RESET_HANDLER_SIZE);
 
-	memcpy(iram_base, (void *)__tegra_cpu_reset_handler_start,
+	memcpy_toio(iram_base, (void *)__tegra_cpu_reset_handler_start,
 			tegra_cpu_reset_handler_size);
 
 	err = call_firmware_op(set_cpu_boot_addr, 0, reset_address);
-- 
2.39.5