[PATCH] RAS: Fix out-of-range section_length in ARM processor error handling

[Abbott Liu]

Commit 87880af2d24e ("APEI/GHES: ARM processor Error: don't go past
allocated memory") added bounds checks for malformed ARM processor
error records but contained several bugs:

- In log_arm_hw_error(), the ctx_info bounds check is inverted. The
  condition `sz + (long)ctx_info - (long)err >= err->section_length`
  adds ctx_info->size when the context header is already past the end
  of the section instead of when it is within bounds. So change the
  comparison to <=.

- The vsei_len < 0 error path did not verify the pei_len and ctx_len.
  When vsei_len is negative, section_length is too small to hold the
  full record, yet pei_len and ctx_len were derived from
  err_info_num/context_info_num and may describe regions beyond the
  (long)err .. err + section_length buffer. To prevent trace_arm_event
  from reading past the allocated record, sanitize the parameters:
  move the cpu lookup above this path so it is available for tracing,
  recalculate ctx_len and pei_len based on section_length, limit them,
  set the corresponding pointers to NULL and lengths to 0  when there
  is no remaining space.

Fixes: 87880af2d24e ("APEI/GHES: ARM processor Error: don't go past allocated memory")
Signed-off-by: Abbott Liu <liuwenliang@xxxxxxxxxx>
---
 drivers/ras/ras.c | 34 ++++++++++++++++++++++------------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/drivers/ras/ras.c b/drivers/ras/ras.c
index 03df3db62334..e37bf11d0926 100644
--- a/drivers/ras/ras.c
+++ b/drivers/ras/ras.c
@@ -58,10 +58,10 @@ void log_arm_hw_error(struct cper_sec_proc_arm *err, const u8 sev)
 	struct cper_arm_err_info *err_info;
 	struct cper_arm_ctx_info *ctx_info;
 	u8 *ven_err_data;
-	u32 ctx_len = 0;
+	s32 ctx_len = 0;
 	int n, sz, cpu;
 	s32 vsei_len;
-	u32 pei_len;
+	s32 pei_len;
 	u8 *pei_err, *ctx_err;
 
 	pei_len = sizeof(struct cper_arm_err_info) * err->err_info_num;
@@ -74,27 +74,37 @@ void log_arm_hw_error(struct cper_sec_proc_arm *err, const u8 sev)
 	for (n = 0; n < err->context_info_num; n++) {
 		sz = sizeof(struct cper_arm_ctx_info);
 
-		if (sz + (long)ctx_info - (long)err >= err->section_length)
+		if (sz + (long)ctx_info - (long)err <= err->section_length)
 			sz += ctx_info->size;
-
 		ctx_info = (struct cper_arm_ctx_info *)((long)ctx_info + sz);
 		ctx_len += sz;
 	}
 
+	cpu = GET_LOGICAL_INDEX(err->mpidr);
+	if (cpu < 0)
+		cpu = -1;
+
 	vsei_len = err->section_length - (sizeof(struct cper_sec_proc_arm) + pei_len + ctx_len);
 	if (vsei_len < 0) {
 		pr_warn(FW_BUG "section length: %d\n", err->section_length);
 		pr_warn(FW_BUG "section length is too small\n");
 		pr_warn(FW_BUG "firmware-generated error record is incorrect\n");
 		vsei_len = 0;
-	}
-	ven_err_data = (u8 *)ctx_info;
-
-	cpu = GET_LOGICAL_INDEX(err->mpidr);
-	if (cpu < 0)
-		cpu = -1;
-
-	trace_arm_event(err, pei_err, pei_len, ctx_err, ctx_len,
+		ven_err_data = NULL;
+		ctx_len = err->section_length - (sizeof(struct cper_sec_proc_arm) + pei_len);
+		if (ctx_len < 0) {
+			ctx_len = 0;
+			ctx_err = NULL;
+			pei_len = err->section_length - sizeof(struct cper_sec_proc_arm);
+			if (pei_len < 0) {
+				pei_len = 0;
+				pei_err = NULL;
+			}
+		}
+	} else
+		ven_err_data = (u8 *)ctx_info;
+
+	trace_arm_event(err, pei_err, (u32)pei_len, ctx_err, (u32)ctx_len,
 			ven_err_data, (u32)vsei_len, sev, cpu);
 }
 
-- 
2.43.0