[PATCH v3] PCI/AER: Map a raw AER Capability image field by field

[Dave Jiang <dave.jiang@intel.com>]

struct aer_capability_regs is not the hardware layout: the embedded
struct pcie_tlp_log spans 60 bytes where the Header Log it stands in for
is 16, so a flat copy misplaces everything behind it.

extlog_print_pcie(), ghes_handle_aer() and cxl_rch_get_aer_info() work
around that by stopping at the Header Log, dropping everything past
offset 44. Flit mode is never decoded either: the Flit bit and Logged
TLP Size sit at offset 0x18, unread, so the Flit DWORDs at 0x38 are lost
and the log prints as non-Flit.

Add aer_cap_regs_unpack() to map the registers individually, taking the
TLP Log layout from the Flit bit as pcie_read_tlp_log() does. Clamp the
logged length: Logged TLP Size is 5 bits wide, so an untrusted value
reaches 31 where dw[] holds 14 and pcie_print_tlp_log() walks
header_len unbounded.

Take the image little-endian, as both sources are: CPER by definition,
PCIe registers on the wire. Read it with get_unaligned_le32(), since a
CPER section sits wherever firmware put it, and take the two source IDs
out of the Error Source Identification register by bit position rather
than byte offset. cxl_rch_get_aer_info() uses readl(), so it hands back
__le32.

Convert all three callers. cxl_rch_get_aer_info() now reads the whole
MMIO block, so size its ioremap by the hardware registers (96 bytes)
rather than by sizeof(struct aer_capability_regs) (100). Shrinking the
mapping is safe: the read it replaces stopped at 44 bytes.

Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260904172337.1409775-1-dave.jiang@intel.com?part=5
Link: https://lore.kernel.org/linux-cxl/CAJZ5v0hDv11cPuztPZsaDd7uwD_49KznJy=tzuRO+dZc=CnAEQ@mail.gmail.com/
Assisted-by: LLM
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

---
v3 (sashiko-bot):
- Give the helper one endianness. v2 fed it a little-endian CPER stream
  and a host-order readl() array, so on big-endian the 16-bit source IDs
  came out of the wrong half of the register. No change on little-endian.

Depends on "[PATCH v6 00/13] ACPI: APEI: GHES: Collection of fixes for
issues reported by sashiko", now picked up by Rafael; please apply after
it. Patches 5 and 12 are build dependencies - this rewrites the aer_info
copies they add - and patch 7 is functional: without its
ACPI_APEI_PCIEAER guard fix, extlog_print_pcie() compiles out. The
drivers/pci and drivers/cxl changes are independent.

No Fixes: tag on purpose. Patches 5 and 12 closed the out-of-bounds
reads; what is left is diagnostic completeness, and this adds an
exported helper and rewrites three call sites.

This is the follow-up Rafael asked for in the Link: above, and also
covers the pre-existing ras_rch.c findings reported there.
---
 drivers/acpi/acpi_extlog.c | 14 +-----
 drivers/acpi/apei/ghes.c   | 15 +------
 drivers/cxl/core/ras_rch.c | 27 ++++--------
 drivers/pci/pcie/tlp.c     | 88 ++++++++++++++++++++++++++++++++++++++
 include/linux/aer.h        |  9 ++++
 5 files changed, 107 insertions(+), 46 deletions(-)

diff --git a/drivers/acpi/acpi_extlog.c b/drivers/acpi/acpi_extlog.c
index 9e61354a807b..bf5f7b1a9aea 100644
--- a/drivers/acpi/acpi_extlog.c
+++ b/drivers/acpi/acpi_extlog.c
@@ -156,19 +156,7 @@ static void extlog_print_pcie(struct cper_sec_pcie *pcie_err,
 
 	aer_severity = cper_severity_to_aer(severity);
 
-	/*
-	 * struct pcie_tlp_log is larger than the hardware layout, so aer_info
-	 * only maps onto the struct up to the four Header Log DWORDs. Copy that
-	 * much, then place the TLP Prefix Log from where the hardware keeps it.
-	 * Everything else stays zero: nothing reads root_command, root_status or
-	 * the error source IDs, and header_len and flit are software-only.
-	 */
-	memcpy(&aer_regs, pcie_err->aer_info,
-	       offsetof(struct aer_capability_regs, header_log) +
-	       PCIE_STD_NUM_TLP_HEADERLOG * sizeof(u32));
-	memcpy(aer_regs.header_log.prefix,
-	       pcie_err->aer_info + PCI_ERR_PREFIX_LOG,
-	       sizeof(aer_regs.header_log.prefix));
+	aer_cap_regs_unpack(&aer_regs, pcie_err->aer_info, sizeof(pcie_err->aer_info));
 
 	domain = pcie_err->device_id.segment;
 	bus = pcie_err->device_id.bus;
diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 08c985e729d6..ade1cc8c9f8d 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -668,20 +668,7 @@ static void ghes_handle_aer(struct acpi_hest_generic_data *gdata)
 		if (!aer_info)
 			return;
 
-		/*
-		 * Map aer_info onto the struct as extlog_print_pcie() does:
-		 * copy up to the four Header Log DWORDs, then place the TLP
-		 * Prefix Log from where the hardware keeps it. The rest stays
-		 * zero, so firmware cannot drive the pcie_print_tlp_log() loop
-		 * over dw[] out of bounds.
-		 */
-		memset(aer_info, 0, sizeof(struct aer_capability_regs));
-		memcpy(aer_info, pcie_err->aer_info,
-		       offsetof(struct aer_capability_regs, header_log) +
-		       PCIE_STD_NUM_TLP_HEADERLOG * sizeof(u32));
-		memcpy(aer_info->header_log.prefix,
-		       pcie_err->aer_info + PCI_ERR_PREFIX_LOG,
-		       sizeof(aer_info->header_log.prefix));
+		aer_cap_regs_unpack(aer_info, pcie_err->aer_info, sizeof(pcie_err->aer_info));
 
 		aer_recover_queue(pcie_err->device_id.segment,
 				  pcie_err->device_id.bus,
diff --git a/drivers/cxl/core/ras_rch.c b/drivers/cxl/core/ras_rch.c
index e0e01aa5eba6..50abbdc80722 100644
--- a/drivers/cxl/core/ras_rch.c
+++ b/drivers/cxl/core/ras_rch.c
@@ -19,7 +19,7 @@ void cxl_dport_map_rch_aer(struct cxl_dport *dport)
 		aer_phys = aer_cap + dport->rcrb.base;
 		dport->regs.dport_aer =
 			devm_cxl_iomap_block(host, aer_phys,
-					     sizeof(struct aer_capability_regs));
+					     PCIE_AER_CAP_HW_SIZE);
 	}
 }
 
@@ -58,31 +58,20 @@ void cxl_disable_rch_root_ints(struct cxl_dport *dport)
 static bool cxl_rch_get_aer_info(void __iomem *aer_base,
 				 struct aer_capability_regs *aer_regs)
 {
-	/*
-	 * Bound the copy to the physically-defined AER registers (header
-	 * through the 16-byte Header Log). struct aer_capability_regs is a
-	 * software layout whose embedded struct pcie_tlp_log is larger than
-	 * the on-wire AER capability; copying sizeof(*aer_regs) would
-	 * over-read the RCRB-mapped MMIO block.
-	 */
-	int read_cnt = (PCI_ERR_HEADER_LOG + 16) / sizeof(u32);
-	u32 *aer_regs_buf = (u32 *)aer_regs;
-	int n;
+	/* A flat copy cannot fill the struct; aer_cap_regs_unpack() places it. */
+	__le32 raw[PCIE_AER_CAP_HW_SIZE / sizeof(__le32)];
 
 	if (!aer_base)
 		return false;
 
 	/*
-	 * Zero the destination so the software-only tail fields
-	 * (e.g. header_log.header_len) are deterministic rather than
-	 * left as uninitialized stack, which could drive a bogus loop
-	 * length in pcie_print_tlp_log().
+	 * Use readl() to guarantee 32-bit accesses; it returns host order, so
+	 * put the registers back little-endian for aer_cap_regs_unpack().
 	 */
-	memset(aer_regs, 0, sizeof(*aer_regs));
+	for (int n = 0; n < ARRAY_SIZE(raw); n++)
+		raw[n] = cpu_to_le32(readl(aer_base + n * sizeof(u32)));
 
-	/* Use readl() to guarantee 32-bit accesses */
-	for (n = 0; n < read_cnt; n++)
-		aer_regs_buf[n] = readl(aer_base + n * sizeof(u32));
+	aer_cap_regs_unpack(aer_regs, raw, sizeof(raw));
 
 	writel(aer_regs->uncor_status, aer_base + PCI_ERR_UNCOR_STATUS);
 	writel(aer_regs->cor_status, aer_base + PCI_ERR_COR_STATUS);
diff --git a/drivers/pci/pcie/tlp.c b/drivers/pci/pcie/tlp.c
index 71f8fc9ea2ed..7f94a09ac7c7 100644
--- a/drivers/pci/pcie/tlp.c
+++ b/drivers/pci/pcie/tlp.c
@@ -8,8 +8,11 @@
 #include <linux/aer.h>
 #include <linux/array_size.h>
 #include <linux/bitfield.h>
+#include <linux/build_bug.h>
+#include <linux/minmax.h>
 #include <linux/pci.h>
 #include <linux/string.h>
+#include <linux/unaligned.h>
 
 #include "../pci.h"
 
@@ -92,6 +95,91 @@ int pcie_read_tlp_log(struct pci_dev *dev, int where, int where2,
 	return 0;
 }
 
+/* The Prefix Log registers hold dw[4..13] in Flit mode. */
+static_assert((PCI_ERR_PREFIX_LOG +
+	       (PCIE_STD_MAX_TLP_HEADERLOG - PCIE_STD_NUM_TLP_HEADERLOG) *
+	       sizeof(u32)) == PCIE_AER_CAP_HW_SIZE);
+
+/**
+ * aer_cap_regs_unpack - Convert a raw AER Capability image to the kernel layout
+ * @regs: Destination, fully initialised
+ * @raw: AER Capability register block in hardware order, little-endian
+ * @raw_len: Bytes readable at @raw
+ *
+ * struct aer_capability_regs is not the hardware layout: struct pcie_tlp_log
+ * spans 60 bytes where the Header Log it stands in for is 16, so a flat copy
+ * misplaces everything behind it. Map the registers one by one instead,
+ * taking the TLP Log layout from the Flit bit as pcie_read_tlp_log() does.
+ *
+ * @raw is not necessarily aligned. Registers past @raw_len are left zero, so
+ * a short image cannot be read past.
+ */
+void aer_cap_regs_unpack(struct aer_capability_regs *regs, const void *raw,
+			 size_t raw_len)
+{
+	unsigned int i, tlp_len;
+	bool flit;
+
+	memset(regs, 0, sizeof(*regs));
+
+	if (raw_len < PCI_ERR_HEADER_LOG)
+		return;
+
+	/* The Extended Capability Header, at offset 0, has no define */
+	regs->header = get_unaligned_le32(raw);
+	regs->uncor_status = get_unaligned_le32(raw + PCI_ERR_UNCOR_STATUS);
+	regs->uncor_mask = get_unaligned_le32(raw + PCI_ERR_UNCOR_MASK);
+	regs->uncor_severity = get_unaligned_le32(raw + PCI_ERR_UNCOR_SEVER);
+	regs->cor_status = get_unaligned_le32(raw + PCI_ERR_COR_STATUS);
+	regs->cor_mask = get_unaligned_le32(raw + PCI_ERR_COR_MASK);
+	regs->cap_control = get_unaligned_le32(raw + PCI_ERR_CAP);
+
+	flit = FIELD_GET(PCI_ERR_CAP_TLP_LOG_FLIT, regs->cap_control);
+	if (flit) {
+		tlp_len = FIELD_GET(PCI_ERR_CAP_TLP_LOG_SIZE, regs->cap_control);
+	} else {
+		/*
+		 * dw[4..7] alias the Prefix Log. Take all four whatever
+		 * eetlp_prefix_max says; pcie_print_tlp_log() stops at the
+		 * first zero one.
+		 */
+		tlp_len = PCIE_STD_NUM_TLP_HEADERLOG + PCIE_STD_MAX_TLP_PREFIXLOG;
+	}
+
+	tlp_len = min(tlp_len, ARRAY_SIZE(regs->header_log.dw));
+
+	for (i = 0; i < tlp_len; i++) {
+		unsigned int off;
+
+		if (i < PCIE_STD_NUM_TLP_HEADERLOG)
+			off = PCI_ERR_HEADER_LOG + i * sizeof(u32);
+		else
+			off = PCI_ERR_PREFIX_LOG +
+			      (i - PCIE_STD_NUM_TLP_HEADERLOG) * sizeof(u32);
+
+		if (off + sizeof(u32) > raw_len)
+			break;
+		regs->header_log.dw[i] = get_unaligned_le32(raw + off);
+	}
+
+	/* @i may be short of tlp_len; non-Flit needs the TLP parsed, so cap at 4 */
+	regs->header_log.header_len = flit ? i : min(i, PCIE_STD_NUM_TLP_HEADERLOG);
+	regs->header_log.flit = flit;
+
+	if (raw_len >= PCI_ERR_ROOT_COMMAND + sizeof(u32))
+		regs->root_command = get_unaligned_le32(raw + PCI_ERR_ROOT_COMMAND);
+	if (raw_len >= PCI_ERR_ROOT_STATUS + sizeof(u32))
+		regs->root_status = get_unaligned_le32(raw + PCI_ERR_ROOT_STATUS);
+	if (raw_len >= PCI_ERR_ROOT_ERR_SRC + sizeof(u32)) {
+		u32 src = get_unaligned_le32(raw + PCI_ERR_ROOT_ERR_SRC);
+
+		/* One register: ERR_COR in 15:0, ERR_FATAL/NONFATAL in 31:16 */
+		regs->cor_err_source = src;
+		regs->uncor_err_source = src >> 16;
+	}
+}
+EXPORT_SYMBOL_GPL(aer_cap_regs_unpack);
+
 #define EE_PREFIX_STR " E-E Prefixes:"
 
 /**
diff --git a/include/linux/aer.h b/include/linux/aer.h
index df0f5c382286..043ee76b6f53 100644
--- a/include/linux/aer.h
+++ b/include/linux/aer.h
@@ -24,6 +24,13 @@
 #define PCIE_STD_MAX_TLP_PREFIXLOG     4
 #define PCIE_STD_MAX_TLP_HEADERLOG	(PCIE_STD_NUM_TLP_HEADERLOG + 10)
 
+/*
+ * Size of the AER Capability register block in hardware, long enough for the
+ * longest Flit mode TLP Log. struct aer_capability_regs below is larger and
+ * laid out differently; use aer_cap_regs_unpack() to convert.
+ */
+#define PCIE_AER_CAP_HW_SIZE		96
+
 struct pci_dev;
 
 struct pcie_tlp_log {
@@ -68,6 +75,8 @@ static inline void pci_aer_unmask_internal_errors(struct pci_dev *dev) { }
 
 void pci_print_aer(struct pci_dev *dev, int aer_severity,
 		    struct aer_capability_regs *aer);
+void aer_cap_regs_unpack(struct aer_capability_regs *regs, const void *raw,
+			 size_t raw_len);
 int cper_severity_to_aer(int cper_severity);
 void aer_recover_queue(int domain, unsigned int bus, unsigned int devfn,
 		       int severity, struct aer_capability_regs *aer_regs);

base-commit: 86adf9d0f7b074e0a1310c1bc4db66cac5c83eec
-- 
2.54.0